Pablo14

I have a 1993 Nissan Sentra GA16DE automatic, that is showing an erratic idle problem.

The main local dealer , after around 4 visits, detected the problem and their tech suggested the replacement of the Idle Air Adjusting Unit, located behind the pcv valve a little to the left, with a screw at its front.

But this doesn't solved the problem. At the dealer someone suggested visiting an independent mechanic who worked at the dealer for a couple of years and I went to this mechanic and he wasn't able even to detect the problem. Well, he didn't asked for any pay for its work, but I found it strange he wasn't able to see the problem because when I went to pick my car from its shop, unfortunately it was closed already and he wasn't around, my car was showing the problem.

Someone suggested mechanics don't like to work on this kind of problems because it is time consuming and they can make more money in less time working with other more conventional vehicle repairs, and I believe this is true even if is not the case with this independent mechanic. At least, that is the case probably with the dealer because of the method they use to pay the mechanics, according to what I recently learned.

The end result is that my 1993 Sentra continues with the problem since it was 139,949 miles. It started with a sudden problem that made the spark plugs turn black with carbon, I replaced the plugs and the problem was there again about a couple of thousands miles later. The car was presenting a pattern as if I was accelerating the car myself and removing my foot from the accelerator when I was not doing anything, but it was occasionally, not always.

After re-installing the original a/c compressor the problem turned to be worst, and now almost all the time the erratic idle appears, dissapearing after a couple of minutes of driving. The car is now more than 154,000 miles. It is close to one year with the problem.

A list of things replaced: Oxygen Sensor, Coolant Sensor, Idle Air Adjusting Unit (two valves in one), Rotor, distributor cap, spark plug cables, sparks (NGK originals), fuel and air filter, pcv valve, and the radiator which probably is not related. Nothing else.

I can go back to the dealer and ask for help because they installed the Idle Air Adjusting Unit, but the fact is I think the dealer is doing a poor job, probably because of what I wrote above. Thanks.

 

Joshb13sentra

An erratic idle can be caused by a number of things. I doubt the AAC valve (what you are talking about) was bad most of the time they just get crapped up and can be cleaned.
Check out your TPS They go bad and/ or it may be out of ajustment. Sentra.net has a list of things that may help your car check there also.
Take the throttle body off and clean it make sure you clean out the little vacuum hole behind the butterfly valve.
Get a vacuum gauge and make sure your lines are all good. There are more but I can't think right now.
I'm sure others will give suggestions.
Hope this helps
Josh

javierb14

erratic meaning it sounds rough, searches for an idle, or idles high?

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Pablo14

Thanks to both of you who answered.

I decided to ask for help again to the same independent mechanic and he was trying to find vaccum leaks.

Also, he removed the new AAC valve to check inside the manifold
where it is connected. He cleaned the area, with a pressure hose without removing the part, and adjusted again using the
idle adjusting screw of the AAC valve.(I think he opened a little, probably allowing more air) The car is better, but it still sounds a little strange, too low rpm at idle, and not enough rpm when the a/c compressor starts working or the two electric radiator fans.

He suggested that I could visit another independent mechanic who also worked at the dealer before.

This other technician has better equipment for the diagnostics
of my 1993 Sentra , described by the first tech. as something defective that is oscillating, making the rpm of the car oscillate
too.

I still believe he could have done as you say, removing more parts from the car and checking more deeply, but I also believe
he was thinking. There's a possibility that after doing that
something else is wrong and how is he going to ask for money
if the repair can't be completed?

So probably, the time + money = repair equation was incomplete and he decided not to go for it because he might find something else he can't detect. It is a business and he has other, more productive and conventional repairs waiting. My car's condition is not business for him.

Regarding the AAC valve, a dealer tech. suggested first no to buy
the part unless the car failed again, and I think he also said he cleaned the old AAC valve. But the car wasn't good after this and I decided to buy it.

The second technician has apparently every certification available,(I saw his office wall full of certifications, including the Master Tech.) or close to it and he was the supervisor at the dealer. Maybe that is why he has more money to buy more expensive equipment than the others, and he will charge $40 for the inspection and the diagnostics only....

At his office's wall below the certifications, I read a paper saying:
" Here we work with love and art, but not for the love of art...."

Pablo14

Update:

The second independent mechanic I talked about in my post above FOUND NOTHING WRONG WITH MY SENTRA!!!!

He used a $7,000 new and advanced computer scanner equipment which he bought last December 28 2002 .
After cleaning the throttle body and checking if the throttle position sensor was ok with another equipment as well as other few things, he did what is called the basic adjustment for my 1993 Sentra, which requires an ignition/distributor adjustment of 10 degrees +/- 2 degrees.

Because my Sentra has a tendency to make too much engine knock using the 10 degrees adjustment, I asked this second tech. to retard the timing as many others do in this cases and I think is universally recommended.

The tech. said is better to retard just 2 degrees, but at the same time he suggested that usually retarding 2 degrees is not enough, so he decided to retard 4 degrees, down to 6.

He also suggested that in a near future, at least the EGR valves should be cleaned, and maybe if the knock problem increases again, removing the cylinder head for cleaning and repairs, and a visit to the machine shop will be required. He asked if the check engine light has ever work and I told him that I have never see it on while driving, only when the vehicle starts and that is normal, because it turns off by itself.

My 1993 Sentra GA16DE engine is almost 155,000 miles and counting and also, it was not build in Japan or the U.S. but in the Nissan Plant of Aguas Calientes, located in Mexico. Yes, a "Mexican Sentra".

Some people think the ones from Japan are better........and they are probably right. Thanks for reading.

 

mmcg80

One month ago, I receive a Dodge Stratus with the same problem. The cure was the spark plugs wires replacement and vacuum problem with the manifold.
But I have a mexican Sentra and I experimented with him, and the only part who makes a similar failure is advance timing to 20 degrees.

But you can make a plan to solve the problem.
1.- Back to the scanner codes
2.- Check the failures codes
3.- Check in your scanner the Park/Neutral screen. Must be change when shift from Neutral to Reverse or 1st gear
4.- Check all vacuum hoses
5.- Check the engine parameters and send me
I hope, this is a cure for your´problem

SergioCR

One thing that nobody checks... a friend of mine had some weird problems when accelerating, the car looses power when it was accelerated and eventually dies when going uphill... i thought it was the fuel pressure too low or a vaccum leak somewhere but the problem ended on having a full of oil distributor cap and crank angle sensor... probably the oil inside the sensor made the computer "think" that the engine was not moving since the photosensors were blocked by dark oil... the o-rings on the distributor shaft were burned so the engine oil went staight to the dist. We changed the whole distributor and the problem got solved.

Pablo14

I am online now, and received your message.

My car is better right now, but the terrible Summer Heat
started in this island on March 18.

My car, well, it has now more than 157,000 miles.

I noted too that some "sweat" of oil or oil are present
in the bottom of the distributor, but not inside the distributor.

Because it is exterior, I think it is due to some oil gasket, like
the one of the engine block, requiring replacing.

I replaced oil gasket from the valve train or cover years ago.

And, I tight the bolts of the valve cover in the order the big manual suggests, from time to time.

Yes, I think eventually I will have the problem you suggested
in your reply, because of the excessive heat and mileage, for the climate in which I use the vehicle of course.

Other people might say that close to 160,000 miles is just
the "break in period of a car" and I agree, but in this
hot climate, with too much traffic congestions, I am going
to tell you what I do.

Usually, I took highway trips, when I can, just for fun, because
is healthy for the engine of this Sentra.

Of course, I am risking a lot because the engine is old, or
more exactly , close to 158,000 miles old............and things
could happen, like a sudden failure of anything when I found
myself far away at the highway, 70 or more miles away...


Thanks for your response.

Myetball

I had an erratic idle in my E16 it seems like forever. Tried everything and it was constant and nothing seemed to work. Then one wonderful day I blew a head gasket. When I picked up the head from the shop they told me 5 of 8 valves were replaced due to excessive pitting. Since I put it back together the erratic idle is completely gone.

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Pablo14

Thanks Myetball too,

I also thinks the multi-valve system must be at a point where
it might require repairs.

I am trying to see how far this engine could go without having
to open it for moderate or major repairs.

I use on it synthetic oil since it was new, even after reading
the bad news about the new type of "cheap synthetic oil", so
I use Amsoil on it since the engine was close to 143,000 miles.

One of the technicians who drove it said the car runs like new, but probably it will require repairs too on those valves, probably due to the high rpm the engine require for almost anything, unlike the 2000-03 Sentra

Thanks for your response, again

 

SergioCR

Hi, well, 157K on a GA should be ok.... it is a great durable engine...

Have you checked the timing?

Just to be sure, with engine off and cool unbolt the whole distributor out and check the inner o-rings (or replace them) make sure to have an automotive parts shop available since the car wont move whithout dist.
also remove the rotor and being very careful remove the dist. seal and the metal plate that covers the crank angle sensor, it is located inside the metal part of the distributor. Should look perfectly clean.

Pablo14

The timing was checked by two different techs.

They did an adjustment called the basic, in which the car's timing
in this case is set to 8 or 10 degrees.

With that adjustment, since the car was new, the engine has
a tendency to make that engine knock we all hate to death.

So, two Nissan techs. decided to use a lower setting.

Actually, both techs worked for the main local Nissan dealer.

One of them, used a 5° setting, but the other said that was
too low, and I think he chose a 6° or 7° setting and that is what
the car has right now. Engine knock is reduced to a minimum, or
light knock is audible under severe conditions only.

This engine knock problem is what I may call the only problem with this car, the rest is considered by anyone else mostly routine.
(the car was made in Mexico, by the way....)

By the way, the car is original, everything, except the oil........

Thanks for your answer. (I am not going to remove the distributor until is necessary)

Pablo14

Thanks mmcg80.

It was today that I read your response, maybe because the
email response for your reply never arrived.

Your response is the most technical of all, and there is where
I am a complete failure.

I have no scanner available..........., but the car was checked
twice by two independent technicians, and the dealer......

I believe all of you have part of the answer, honestly.

Because the engine has mileage, and it runs at high rpm,
all of what you say will occur, if is not already there yet.

I am trying to see how far in terms of mileage it will run
before it is absolutely necessary to open it for moderate
or major repairs.....

Maybe, I am asking for too much........., if you ask the dealer
they will say of course.........they want to sell new cars!

Thanks again, mmcg80

Mack

Wow...it's too bad you're having this much trouble with the idle. My 93's idle problem went away after the usual - fuel filter/O2 sensor/spark plug/throttle body clean - type tune up. It's a frustrating problem - I struggled with mine for only a couple months and that seemed like an awfully long time.

I don't think this is an answer to your problem, but I do think that it could help a little. While my car was idling so irregularly (and dying a lot) I put fuel injector cleaner in with every few gas tank fills. I went for the premium line of STP because it was expensive (ha) and I thought it would work better. Well, it did. For a couple months, it was the only reason my car idled at all. Maybe you could use it a few times in addition to all the parts you've replaced or cleaned and see if it helps. Even if it doesn't help the idle much it will clean your injectors a little.

Good luck. Maybe you could keep us posted on what works for you - I'm sure that there are plenty of frantic GA owners who'd like to know what's up with their idle.

__________________
1993 Sentra XE
5 Speed 2 Door

Pablo14

Believe it or not, I was thinking about fuel injector cleaners too,
but in a way you can't imagine, probably.

Because a few of the recognized top mechanics around were
not able to detect what was making the rpm go up an down,
I started thinking about what else was left, and it all ended looking at myself......the only "machine" which was not scanned.....

I usually buy a bottle or two of Techron Concentrate every time
I change the oil and the filter of the car, so my car uses fuel
injector cleaner, but I also noticed that I have another thing.

Always, I fill the fuel tank of the car all the way to the top, until
you can see the fuel's color, if any, in this case no color at all
because I buy premium 93 always.....unless the gas stations cheats, sellling regular instead of premium.

I read at other car owner's manuals that this is not recommended, specially at one of the new Honda Odyssey.

You might say, what my car has to do with a new Honda Odyssey?

The tank, yes the fuel tank.

Fuel tanks are similar in some way.

By filling the tank too much, or overfilling, which is not recommended by Honda you create problems, I actually
can't explain in details.......sorry.

You know how I ended looking at an Honda's manual?

I found the new 240 hp Honda Odyssey has a little
fuel tank, for the amount of fuel it uses, having the
wheels aligned, proper tire pressure and everything.

The owner of that minivan was noticing too many
fill-ups where required and I checked the manual
and found that its tank makes around 75.7 liters or
20 gallons of capacity,...

.. meaning that you'll have to buy around 17.3 gallons in order to fill it everytime, which is a liitle amount, considering the minivan weights alone more than 5,000 pound, has 240 hp, and moms use that DVD all the time to entertain the kids while
leaving the minivan at idle a lot......... (My Sentra has
a sticker which says it weights 3,318 lbs)

Honda suggests not to overfill, but I overfill the
tank of my Sentra for the same reason that some
people started overfilling the one of the Odyssey:
the tank is little, 13.2 gallons total, and with the
a/c on fuel mileage drops with the automatic
transmission to 26 mpg in the city or actually less.....giving you
low range of miles in traffic.

You might say: don't use the a/c and don't overfill !!!!!!!!!!!!!!!

Of course.......if only I was living in one of your
cool states....I am living in an island where
serious heat started this year on March 18 and it
might continue up to December 31!!!! It might go away
on November or at the end of October..

Anyway, I think that by always, read well, always, overfilling
the tank in order to take fuel economy averages, I always
remove the dirt from the bottom of the tank and at some
point it might go to the injectors, filter and whatever....

I replaced everything you say, including the filters and a
couple of sensors, like the coolant and oxigen sensors.

The coolant sensor failure was indicated by a Nissan Consult
scanner at the dealer.......

And, I used an intensive treatment with Techron Concentrate.

My car seems to be fine now, but I still think it is a low at idle,
but that is due to the 6° setting of the ignition timing.....

But, well the car is close to 160,000 miles..............no major
repairs yet to the engine, and the transmission has received
oil changes only.

I hope my car reaches 200,000 miles without major repairs,
but maybe I am asking for too much for a high rpm engine.

Others suggested, valves replacement, machine shops,
one of the techs said the EGR's must be cleaned too
(at a cost of $60....)

Thanks again, Mack.................