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I am experiencing low/rough idle after replacing my cylinder head. The engine doesn't seem to be misfiring as it revs up well and drives fine under hard and normal acceleration. It just seems to idle low and rough when in "Drive" at the lights. No engine light on. I have replaced the spark plugs, all new gaskets with the head, cleaned throttle body and tried another temp sensor.

I have tried the Idle re-learn, throttle valve position procedures. I think they completed successfully but no change in the idle.

Has anyone experienced a similar issue after replacing their head gasket or cleaning TPS? I read somewhere that the dealer or someone with a decent scan tool needs to reset the idle or ecu?

Any help would be much appreciated. Cheers
 

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One of the first things to do is perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction. If you have a copy of the FSM for your vehicle, the code readout procedure is described there along with a listing of codes. You can download a copy of the FSM sections from the Nico Club web site; here's the URL: http://www.********.com/FSM/ (replace the asterisks with "nico club" spelled as one word). The section EC.PDF is the one you need to read.

The common causes for rough idle are:

- Intake system vacuum leak. 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.
- Dirty fuel injectors.
- EGR valve. Check all the vacuum hose connections.
- Marginal performing Ignition coil.
- Bad spark plug wires or incorrect wiring.
- The cam timing may be incorrect.

If you've just replaced a head gasket or if you have a high mileage vehicles with over 100,000 miles are the most likely to start having engine miss problems (it can be less in some vehicles), then it's advisable to have a compression test performed to rule this out. If you have low compression on one or more cylinders, this could be indicative of a more serious condition that would need to be fixed immediately.

The normal procedure for a compression test is to remove all the spark plugs, insert a compression gauge into the spark plug hole, and then turning the engine over about three times. Record the reading and do this for all the cylinders. If there is more than a 20% difference in any of the readings, a further test would be required to determine if the variance problem is due to an issue with the piston rings, the valves or the head gasket.
 

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Great info thanks rogo.

Update: I sprayed water all around the inlet manifold and vacum lines but no change in the idle. Re checked inlet manifold bolt torque.

Disconnected each coil pack. Idle changed for each so definetly firing on all 4.

I have a lot of tools but no scan tool, comp test or vac gauge.

Im going to re check the timing marks tonight even tho im 100% sure it was right. Maybe it some how got a tooth out as i rotated the engine and chain took up slack. At this point i might need to recheck everything. 😔
 

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Timing marks are spot on. Im starting to think the issue is with the second hand head. Might try get a comp test done and codes read.

 
 

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Do you have any new updates? I have the same exact problem. It all started after replacing the head gasket. I have triple checked everything. I am also getting very low gas mileage.
 

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Sup Mod keeping the peace
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Great info thanks rogo.

Update: I sprayed water all around the inlet manifold and vacum lines but no change in the idle. Re checked inlet manifold bolt torque.

Disconnected each coil pack. Idle changed for each so definetly firing on all 4.

I have a lot of tools but no scan tool, comp test or vac gauge.

Im going to re check the timing marks tonight even tho im 100% sure it was right. Maybe it some how got a tooth out as i rotated the engine and chain took up slack. At this point i might need to recheck everything. 😔
Do the same disconnect test on each fuel injector. If that's OK, run a compression test on each cylinder; Standard 192 psi, Minimum 168 psi, maximum allowable difference between cylinders 14 psi. If you find a bad cyl reading, you can follow it up with a leakdown test to determine the cause.
 

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Discussion Starter #7
I never found the issue, it drives well just idles slightly off. I put it down to an issue with the second hand head, maybe a valve not sealing 100%. If you do find the issue if you could let us know that'd be great.
 
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