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Discussion Starter #1
Have a ’98 4WD Frontier, 160K miles.

As of 4 days ago I’ve had occasional stalling on idle (perhaps 1 out of 10 times I stop at a stoplight) and also occasional very brief engine hesitations at cruising speeds, akin to a, say, brief “hiccup” in engine power (perhaps a dozen episodes in a 250 mile trip).

It first happened 200 miles away from home on my 4th of July trip. Not a good situation.

No engine light and no codes (I read them).

Concerned about being left stranded, I tried to debug the thing myself since everything was closed for 4th of July. Ended up suspecting the IACV (Idle Air Control Valve) as something that would likely result in this behavior and would also likely not generate a code. But I did not get anywhere. I just sprayed some carburetor cleaner in the throttle air bypass hole, which seemed to make things a little worse, as it seemed to be stalling more often – but it could have been the higher engine temperature too, after repeated starts. Taking apart to clean the IACV was out of the question since I was going to have to remove the throttle body and did not have spare seals to reassemble (seals would likely rip on disassembly after 17 years).

Concerned about the 200+ mile return trip, I took truck to only garage I found open. Very nice guy, pleasant to work with and seemed competent. After running diagnostics he said the MAF signal was noisy and that Nissan had a TSB about adding an additional ground wire to the MAF sensor. He put the extra ground but things did not improve. So he said it was the electrical connector to the MAF that was faulty (logical). He actually demonstrated to me how with the engine on idle, pressing on the MAF electrical connector caused the engine to stall. Not sure how many times he tried that and whether it might have been a coincidence. Unable to find a connector on Sunday, he tried to fix it by bending a bit the pins and when that did not work trying to insert small wires in the connector to achieve better contact, but that did not work either.

At this point I started suspecting that indeed the problem might be at the MAF but not with the connector. Rather with the MAF itself. I thought it was more logical that the pressure he was applying to the connector somehow transferred inside the MAF and that is where the problem is. Otherwise, I could not see how a marginal connector can be disassembled two, three, five times and always get that marginal connection. Typically futzing with a marginal connector at all makes it either establish contact or drop contact completely. And dropping contact completely would have caused a code (I had tested that myself, removing the MAF connector threw the expected P0100 code and set the computer in safe mode with intentional fuel cutoff above 2000RPM).

In any case, he was not able to fix it, but I successfully made the 200+ mile trip back home, with just one stall on idle at stoplights and about ten “hiccups” at freeway speeds. Otherwise, engine behavior was, I would say, normal, or perhaps near normal overall.

BTW, the mechanic was very nice. I wanted to pay him at least something for the 1.5 hours he spent working on my truck, even if he did not ultimately fix it, but he insisted that he did not want any money since he was unable to fix it. So I left feeling kind of bad -- I thought I should at least buy him a gift next time I go by that area (which I tend to do once a month).

In any case, now that I’m back home I’d like to see if I can fix this problem, so before I do anything I wanted to ask,

Anyone else had similar issues or insights?

A couple of other things I noticed:

No engine light and no codes

Took the spark plugs out on my first diagnostic attempt and they were all 4 darker than usual, not wet but with more carbon than usual. Right before I took spark plugs out truck had been idling for a while and then had stalled by itself. I did not try to look at spark plugs after a normal drive.

Even when the engine is not stalling on idle, the idle speed is sometimes a little erratic, but not always.

Malfunction may be more prominent in hot desert air than cooler moist air. But it’s a rather recent problem, so I’m not sure, could be coincidence.

Starts fine and no problems while engine cold. Any intermittent problems only start after engine has warmed up.

The stall is most repeatable when I rev up engine in neutral and then release the gas and let it go to idle. That is when it typically stalls.

Sometimes as the idle RPM drops below normal, it revs up and recovers.

Fast idle when cold works as expected- also higher RPM when AC on also works as expected

I moved around spark plug wires several times while engine was idling, no difference

I looked at the MAF sensor, looks clean

I intentionally disconnected MAF to see if problem would go away in computer safe mode. Did not completely stall but engine operation without MAF was quite erratic, rough idle and not able to go above 2200 rpm (I think this is expected since computer goes into safe mode). But erratic behavior makes it hard to come to conclusions. I did get the P0100 code disconnecting the MAF, so some error detection is working.

I looked at the IACV (Idle Air Control Valve). I can hear it clicking when I disconnect and reconnect it while ignition on and engine off. Measured correct solenoid resistance ( 10.9ohms). Got the correct codes (P505) when I disconnected it for more than a couple of seconds.

I noticed that the IACV solenoid buzzes just a tad bit with ignition on and engine not running (when everything is quiet). But not a loud buzzing.

My speedometer is sometimes acting funny, showing higher or lower speed than normal (+-20 mph), but this has been going on for quite a while (a year or so) and seems to be unrelated to this stalling problem. Definitely predates it by a long shot.

No other prior major problems. Though a 4 banger I love the truck, has served me well. I maintain it well – myself. Yes, I have had the typical O2 sensor going bad here and there and a couple of minor coolant leaks from 15+ year hoses, all expected.

Thanks for reading.
Any advice appreciated.
 

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Sup Mod keeping the peace
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Several things to check:

- Replace the fuel filter and air filter.
- Check or replace spark plugs. Use only OEM NGK plugs; any other types can cause driveability problems.
- Check the fuel pressure. Tee-in a tempoarary fuel pressure gauge at the output side of the fuel filter. The readings at idle should be as follows:
* with vacuum hose connected to the fuel pressure regulator: 34 psi
* with vacuum hose disconnected from the fuel pressure regulator: 43 psi
- Check for a major vacuum leak in the intake system. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
- The fuel injectors may be dirty. Run some good injection cleaner, like Techron or Redline SL-1, through the system; give the cleaner about a week or two to do it's job.
 

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Discussion Starter #3
I started engine without air filter and focused on the MAFS:

CLEANED MAFS—NO EFFECT:
I cleaned the MAFS with MAFS cleaner (it was a bit dirty after all-had to look at it with magnifying lens) -- no effect. Still stalled at about 10% of stoplights and had more hesitation and sputtering than before. ~10 episodes in a 15 mile trip.

RECREATE STALL BY FUTZING WITH MAF—NO EFFECT:
I cannot recreate the condition the mechanic showed me whereby engine was stalling by pressing on the MAFS electrical contactor. I wiggled/ bent/ pressed on the contactor and its cables, no difference, just a not so healthy idle throughout. Perhaps what the mechanic showed me was just a coincidence at the time.

TRY HOT/COLD AIR ON MAF—NO EFFECT
I alternated blowing hot and cold air on the MAF housing using a blow drier, to test my previous temperature dependence theory. Again no difference. Note: because my MAFS is right on the throttle body I had to cut a piece of cardboard to shield the MAFS air hole from the blow dryer air flow, otherwise if the blow dryer airflow gets close to the MAFS air intake it disturbs the air flow enough to confuse the MAFS and then the engine does indeed stall.

STILL NO CODES.

Rogoman, thanks for the suggestions. Here is my speculative investigation priority at this point:

Spark plugs: I’ll look at them one more time to see if they still show “rich” condition after normal drive. They are NGK. The fact that they were all uniformly showing “rich” condition on my first inspection (see photos below) makes me want to give this low priority. Spark plug carbon is likely symptom not cause.
Air filter: Low priority. Filter is still clean, and engine malfunctions the same way even without the air filter.
Fuel filter: Low priority because there is no hesitation under high engine horsepower. Also seems like a clogged filter would be associated more with “lean” combustion, not the “rich” I observe.
Fuel pressure: High priority? High fuel pressure (regulator fail) seems plausible. Would likely cause “rich” combustion.
Pump bad less likely, again that would correlate to “lean”.
Vacuum leak: Low priority? Would’t this also result in “lean” ?
Fuel injectors: Low priority. The fact that all 4 plugs seem uniformly sooted is not consistent. If I saw difference in one or two cylinders only then I would suspect injectors more.

Here is a photo of how spark plugs looked three days ago (Don’t they look “rich”?):


And here is how they looked in 2009 (I regard these as normal looking, right?):


More tests coming…
 

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Sup Mod keeping the peace
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Yes, the plugs do show a rich condition in the first picture; second picture is what they should look like.

It's still possible that all the injectors are dirty and are slightly leaking causing an irregular spray pattern which might be causing incomplete combustion. It won't hurt to run some good injection cleaner.

You might also consider replacing the O2 sensor and the temperature sensor that the ECU uses; a bad temp sensor can definitely create a rich condition.
 

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Discussion Starter #5
Here is how spark plugs look today after 18 mile drive( 10mi freeway + 8mi city). About 10 short episodes of sputtering at highway speeds and two stalls at stoplights.

Do these still indicate “rich” combustion?

 

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Discussion Starter #7
Thanks.
So perhaps I only have rich condition at idle and other instances where throttle is closed. I'll investigate the IACV then...
 

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...occasional stalling on idle (perhaps 1 out of 10 times I stop at a stoplight) and also occasional very brief engine hesitations at cruising speeds, akin to a, say, brief “hiccup” in engine power (perhaps a dozen episodes in a 250 mile trip)
An intermittant EGR problem could cause both problems. The FSM has diagnostic procedures for EGR and also what they call "non-detectable" (by the on-board diagnostics) problems.
 

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Discussion Starter #9
NOISY / UNRELIABLE MAF SIGNAL?

I think I may actually have a noisy / unreliable MAF signal.

Look at this first video.

With the engine NOT running and the ignition on, I taped the MAF air hole at the throttle body with a piece of electrical tape (the MAF in this 98 Frontier is in the throttle body). You can actually see the black strip of electrical tape at the very top of the video.

I inserted a paper clip into the MAF signal pin (the signal that tells the computer what the airflow is) to measure the signal.

In the beginning, the signal out of the MAF is a low 0.76V. This is a low value but I have zero airflow. Not sure what the signal should be with 0 airflow (but I measured the signal at idle and it is within spec).

But now notice what happens when I press both the connector and the MAF housing. The voltage starts fluctuating, sometimes going as high as 1.30 V. I also show how striking the MAF housing makes the signal fluctuate.

I did make sure I had a good connection to the wire through the paper clip and alligator clips, to make sure I was not just measuring bad connections at the measurement apparatus.

So is this normal? Is it normal for the signal to fluctuate like that with the engine not running?

http://youtu.be/-xdD0uazA9Q
 

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The small fluctuation in voltage may be due to an electrical capacitive affect between your body and the signal wires. The signal wires run through a grounded shield; make sure the shield is grounded by checking it with your multimeter.
 

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Discussion Starter #11
Thanks for the pointer rogoman,
But where is the shield? It must stop before it gets all the way to the connector. Should I strip some of the cable's outer plastic or tape to get to it?
I see in the wiring diagram that the shielding is grounded through a connector in the cabin, an enclosure by the passenger feet.
 

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If the engine cable has additional wires besides the MAF signal wires, then it's probably safe to strip the cable's outer plastic or tape wrap without destroying the shield. If the cable has been tampered with, then it's possible that the shield may be damaged. If you're able to access the shield at the MAF harness connector, do a continuity test from the shield to engine ground to insure that it's grounded.
 

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Discussion Starter #13
MAF SIGNAL SHIELDING IS PROPERLY GROUNDED:

I tested the MAF signal cable shielding for proper ground. It seems to be well grounded.
I peeled back the cable wrapping, the shielding started about ½” from the MAF connector.
Shielding is at 0V (well at 0.006V to be exact). Also to verify that I had a good ground I hooked a 7W light bulb ([email protected] 12V) to the battery (+) and grounded it through the shielding and it lit properly. So the ground looks pretty solid.


BUT SCOPE SHOWS NOISY MAF SIGNAL?

In the following video, I borrowed a potable scope to look at the MAF signal. The video shows the MAF signal while I press either on the MAF housing or the MAF connector. The engine is idling most of the time, though I do rev it up in a couple of instances. You can hear the uneven idling (yes I have a noisy belt pulley too).

Other than the electrical noise the MAF signal voltage looks within specs. Specs are 0.9-1.8V at idle and 1.9-2.3V at 2500rpm. As you can see in the video my idle voltage is about 1.6V at idle and 2.2V when engine is revved up.

This MAF signal looks noisy to me. I have never looked at any automotive signals with a scope before, so I don’t know what to expect. But still that much noise does not look normal to me.

https://www.youtube.com/watch?v=0oaSzRDEAwQ
 

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Discussion Starter #14
1) Five days ago, I did a crude test for VACUUM leaks:

I made some contraption with a glass jar and two hoses, lit an olive oil drenched paper towel in the jar, closed it and blew some smoke through the brake booster vacuum line.

I did not see any vacuum leaks, though, admittedly I could not make a lot of smoke this way. But seems to me I should have discovered any major leaks even with this crude device.


2) So (four days ago) I CHANGED THE MAF SENSOR:

Behavior changed, I no longer get the occasional hiccup at cruising speeds but problem with idle persists.

I did not want to buy an OEM MAFS just on suspicion (It is about $400) so I got a cheap one online for about $35, just to try it out.

On the positive side, the new MAFS does not have a noisy signal like my original. When I wiggle and apply pressure on the MAFS electrical connector or the MAFS housing with the engine not running and ignition on, the signal I read with a voltmeter stays constant. Also the new MAFS seems to respond to the engine being revved up -- the voltage increases. I have not looked at the signal with a scope but I’m pretty sure its more stable. Is it more accurate than my old MAFS? Well that I don’t know.

But in any case, with the new MAFS I don’t seem to get the short power hiccups I was experiencing before at cruising speed. I have now driven back and forth 3 times to work (6x20 miles) and no cruising speed hiccups. I used to get 4-5 hiccups per trip before.

However, the idle is still erratic when I go to work, but not when I return! Also, I never get an erratic idle immediately. Certainly not when the engine is warming up (fast idle). But even after the engine reaches operating temperature, still the idle is normal, in the beginning. Then, going to work, after I have driven a good 20’-25’ on the freeway and then continue on city traffic THEN I notice the rough idle at stoplights. Then the idle goes between 800 and 500 rpm and the engine feels like it’s going to stall, but never quite does. No codes! In a way, the rough idle is now worse with this new MAFS, but surprisingly, it never stalls like it used to with the previous MAFS.

Returning from work late in the evening, when the driving pattern is reverse, I get all the way home without any rough idling (idle is not perfect but I would say not pathological in this case). In this reverse driving pattern, I first drive 6 miles on city streets and stoplights and I don’t get any rough idle. The engine reaches operating temperature within the first 2 miles. Then I drive about 12 miles on freeway and then finally 2 miles on city streets and stoplights close to my house. I don’t get any rough idling on these last two miles. Basically I don’t get any rough idling at all on my return trip home.

When I changed the MAFS, I read a pending code P0171 (mixture lean), after one round trip to work (2x20miles). But it was only a pending code, and I think it’s was likely because the new MAFS is different than the old one. I cleared the code and did not get another one in the next two days driving back and forth to work.

In any case, if it were a vacuum leak, it would not take 30’ to manifest itself. Would it? I imagine once the engine warmed up (5mins at most) it would have started causing symptoms. No?


3) So (today) I TOOK APART AND CLEANED THE IACV (Idle Air Control Valve):

Was challenging to remove without removing the throttle body, but with some contortions and McGuyver screwdrivers I managed.

?? Now, QUESTION: is the IACV supposed to stay A LITTLE OPEN when the solenoid is not connected ??

In other words, is the spring inside the IACV supposed to keep the valve completely closed?
Because that was the only thing that struck me perhaps as a little suspicious. The IACV was not completely closed when the solenoid was disconnected.
Otherwise, the IACV did have a small film of carbon deposits but did not seem unusual. I cleaned it with carburetor cleaner anyway.

I also cleaned the fast idle valve, since I was there, and I also took out the four fuel injectors and cleaned them, they did not seem dirty. I put things back together, but still, rough idle after about 20-30 minutes.


4) I DISCONNECTED BATTERY:

And left it disconnected for 30’, just to give the ECU a chance to forget the … traumatic past. Engine was difficult to start afterwards, took 20” cranking before it started, very erratic and slow, then within another 30” it stabilized.

But still, erratic idle after about 30’.

Got another pending code P0171 (lean), but again, I think this might be because the new MAFS likely has different characteristics than the OEM part?


5) I VACUUM PUMPED the EGR with the engine idling:

Engine stalled. So I guess that means the EGR is working?

============================================

Any ideas? Especially whether the IACV is supposed to close all the way when the solenoid is inactive?

Here is a video of the IAVC not closing completely
https://youtu.be/E9Z6HbqpHvQ


And here is a video shaowing me applying on and off voltage to the IACV solenoid (I connect/disconnect the electrical connector)
https://youtu.be/7XAklJn3vQM
 

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1) Easier way to do this is to spray carb cleaner with the engine running...if you can get it to idle smoothly...which it sounds like you can't at the moment...so, nevermind :)

2) Voltmeters do NOT have what I would call a decent response time. Even a good one is only going to update the screen at about 10 times per second, generally less with cheaper meters. If you've got a decent Fluke brand meter with a bargraph at the bottom, that bargraph updates much quicker, but still won't catch the tiny fluctuations. About the only way to check for small fluctuations is with an o'scope.

3) Don't know this one for your model. In general, key off, IACV should be closed.

4) Disconnecting the battery on OBD2 vehicles may or may not work to "forget the traumatic past". Yes, it worked back in the early days of computer controlled cars. Not so much lately.

5) Yep, you got it. Open the EGR, dumps raw exhaust back in thru the intake, engine stalls, or at the very least tries to die.

I think you're might be headed for a fuel pump. Seen lots of cases where everything runs ok early in the day, then goes to crap later in the day after the fuel pump has been run for awhile, and your "lean" code would seem to support that. Only way to tell for sure is to put a fuel pressure gauge on it and watch it...or bite the bullet and swap it regardless.

P.S. I don't own a Pathy, nor have I ever worked on one. Just general engine knowledge.
(And I did stay at a Holiday Inn Express last night :D )
 

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Discussion Starter #16
Thanks jdg,

1) Yes, carb cleaner for vacuum leaks …I have not tried that but I did not mention that I did try the similar propane method. But it does not seem to work. I started by releasing some propane directly into the throttle intake, to see what effect on engine RPM I might expect, but there was almost no effect. It’s as if the ECU immediately senses the extra fuel and immediately readjusts, so there’s not really any noticeable change in RPM – especially since the idle is already uneven. So, I figured, if it does not work with all the propane directly into the intake, what’s the chance I’ll be able to detect a small leak? Also, I’m not sure how much propane is needed. I just used a small plumbing torch on up to max flow (what would essentially make a say 4 inch flame if you lit it). Maybe this propane trick only works on older cars?

2) I know that I cannot really see signal variations with a multimeter. But… my old MAFS had enough of a noise in its signal that I could actually see it even on a voltmeter (with the ignition on, engine not running and a piece of electrical tape over the MAFS air hole the signal should be steady – but with the old MAFS I could see variations on multimeter when I applied pressure on the MAFS connector or its housing) . Since that behavior went away with the new MAFS, I feel safe to assume that the noise was originating inside the MAFS – as opposed to some grounding issue or the ECU. Bottom line: The noisy MAFS may have been one additional cause of rough idle, but apparently not the only issue.

I suspect t my old MAFS has some failing electrical connection inside (solder gone bad). But it does not really look like you can open these things, or at least not without risking destroying them. Without having another MAFS I did not want to risk destroying my only semi-working one. The car becomes barely drivable without a MAFS. Now that I have a secondary MAFS, I may attempt to fix my original OEM part -- especially since the new one does not seem to have the original OEM characteristics (though apparently ECU “learns” to interpret its signal – hence perhaps the initial P0171 “lean” code – but always as a pending code, never a check engine).

BTW, thanks everyone for all the help. Though the problem remains elusive, I feel I’m learning a lot. Hopefully this discussion is not so far off track to be useless to others.
 

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1) Just like you're thinking. The ECU sees the propane and adjusts quicker than you can detect it with your ears. The trick is to force open loop operation, keep the computer from adjusting anything. Disconnect the front O2 sensor or maybe the TPS. That should kick a code and keep the ECU in open loop.

Propane is a nice gas substitute. Carb cleaner isn't...which is why I still use carb cleaner to find leaks.

2) Yep, probably had a MAF with a bad circuit board, or at least a rotten solder joint in there. Relatively common, as far as oddball stuff goes anyways. And ya, usually not open-able without wrecking it.
 

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Discussion Starter #18
STARTED GIVING ME AN OCCASIONAL PENDING CODE P0171 (LEAN) :

Of course now I don’t know if this might be caused by that non OEM cheap MAF I’ve installed (since my original Hitachi MAF seemed to have a noisy signal). But in any case,

I CHANGED THE FRONT O2 SENSOR, no effect:

Thought perhaps a failing sensor would give a lean signal, causing the ECU to exceed acceptable fuel trims and flag an occasional pending P0171. Besides that sensor had 155K miles on it, not a waste changing it, I thought. But since it had no effect, I tried to look again at vacuum leaks,

TESTED FOR VACUUM LEAKS WITH CARBURETOR CLEANER:

Used carburetor cleaner this time, and tried to get the ECU to run in open loop for the test.
I thought I could cause open loop operation by disconnecting a few sensors. So I disconnected the Throttle Position Sensor, the MAF and the front O2 sensor. But the engine refused to run with all three sensors disconnected. I had to re-connect the MAF and with TPS & O2 disconnected it seemed to run, open loop I assume? I could now detect some change in engine pitch when I sprayed carb cleaner directly into the intake.

I sprayed around several places throughout the intake, but because the idle was erratic in the first place, my test was rather inconclusive. There was a rather non descript area where if I sprayed I could somewhat detect a change in engine RPM, but not always. Also, it is possible that the carb cleaner simply evaporated from where it was being sprayed and then rose to be sucked in by the throttle intake airflow. Seems like in order to do a better test I’d have to put some tube / big hose on the throttle intake to make sure carb cleaner fumes don’t find their way in. Anyway, I have to get another can of carb cleaner to repeat the test with a better setup.

BTW, I did open my original MAF, you can cut the black plastic cover (and hope to glue it back together if you manage to fix it). I figured there was likely some bad contact inside or a solder that had gotten loose. But the entire circuit is covered with a tacky sort of silicone or polyurethane gel. Even if I managed to get the gel out, the small wires that attach to the circuitry don’t seem to be soldered. They look like they are almost braised (or something) to the leads.

====================

Well, I have the fuel pressure test left top do. Then I’m probably ready to declare defeat. Have never taken my truck to the dealer, perhaps this is the time I find out whether they’re worth the $150 they want to charge me for diagnosis.
 

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The best way to test for major vacuum leaks is to use a good vacuum gauge. To check the intake system for a vacuum leak, attach the vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here are some vacuum gauge readings and their indications:
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Low & steady: Late ign timing/valve timing, low compression

Very low: Vacuum leak

High & steady: Early ignition timing

Gradual drop in reading from idle to higher RPMs: Excessive back pressure in exhaust system

Intermittent fluctuation at idle: Ignition miss, sticking valve

Needle fluctuates as engine speed increases: Ignition miss, blown head gasket, leaking valve or weak valve spring
 

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Discussion Starter #20
Thanks rogoman,

Well, maybe some data is finally coming up:

I did a crude vacuum test. Below is a video of what is happening with my vacuum. Now I recognize this is probably not the right tool to test vacuum, tomorrow I’ll look for a proper automotive vacuum gauge for the job. As you can also see in the video I hooked the vacuum gauge to the brake booster hose which unfortunately has a valve -- so I had to resort to a hack where I put a paper clip to create some small vacuum release otherwise the valve would simply retain the maximum vacuum.

I see the needle fluctuating which is not a healthy sign, but it could also be an artifact of my gauge and setup. As I said, tomorrow I’ll look for a proper gauge and hook it up to a hose without a vacuum valve.

My Vacuum video:
https://youtu.be/zoohhMJsnCg


Now since fast vacuum fluctuation could be a sticky valve, I did a google search and found this video:
https://www.youtube.com/watch?v=PI5bBV0ZFek

I did this same “paper by the exhaust” test on my truck and lo and behold, this afternoon that I had a sporadic rough idle issue (the idle is not always rough – it’s intermittent) what I saw was: The paper was being pushed back (normal) then at some point it would do a random suction (paper goes toward the exhaust-abnormal) and then immediately after the engine would try to stall -- but would not fully stall, there was a small surge towards more normal RPM and then the idle would recover till the next rough incident, which yesterday evening was about once every 5 seconds. But as I said this rough idle sometimes it’s not there at all, sometimes its mild and sporadic, sometimes is almost constant.

Here is another video I took yesterday evening where perhaps you can hear the sound the exhaust makes when the rough idle malfunction is almost constant. Great Harley sound up close like that! I had not discovered the paper trick yet when I took this video so I don’t know what a paper would have done here.
https://youtu.be/RQTGjkN_xlk

More tests tomorrow…
 
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