A Truly Vexatious Idle Problem

[NC318]

Many people post on here regarding idle problems and are referred to the usual suspects. However, I seem to have one that's truly vexatious:

1. Idle fluctuated noticeably. Not the idle control valve as that's pretty new and functioning properly.

2. Took to mechanic. Informed that various hoses plus the air mass boot are aged and cracked - vacuum leak. Need replacing. "Replace them all," I said.

3. Picked up car, drove off this morning, all seemed fine.

4. However, after about ten minutes of driving when car fully warmed up, the problem occurred again, consistently. This time it's when I punch the cluch it to put the car in neutral as a stop for a light or intersection.

5. The engine, when I depress the clutch, sort of "lugs" or seems to come close to stalling. It then sort of "catches" and the RPM's shoot up significantly. It then smooths out somewhat, but continues to fluctuate sufficiently to notice on the tach and be "felt" in the car.

6. Chagrined, I contacted the mechanic who said it worked fine for him, and was driven warmed up. He then speculated that the air leaks having been stopped, the fuel was now running too RICH instead of too LEAN and the computer was "hunting" for the right setting. He said it might be a minor computer adjustment.

7. What do all of you think? Is he right, or is there something else at work here? Thank you for any suggestions.

[omw41]

If it's truly and idle problem, have you considered the Idle Control Unit? This is located above the glove box on the passenger side. You'll have to take out the glove box and the upper piece that the straps attach to. The ICU is a green box with 12 wires attached to it.

However, the way you described it, it could be fuel delivery, no?

[bbrg86]

i had the same problem and it was a loose plug that regulated the air in the engine, t hought it mihgt have been fuel delivery but my mechanic just pushed this plug in and the problem smoothed out. here are pics of the plug, make sure its properly connected - hope this helps

[NC318]

Thanks much to both of you. The picture was particularly appreciated and I will check out the area promptly.

I do hope it's not the ICU! I seem to recall that is an expensive piece of eqiupment.

[greese]

It's ECU, not ICU. Everyting is connected to the ECU - fuel, air, temp, etc. The plug in the pic is connected to the AFM. There is an ICV (idle control valve) which is the valve with the small hose adjacent to the intake. Both parts cost serious money new, however, both can be cleaned. I cleaned both parts with carb cleaner last week and got a lot of brown guck out of them.
I to had an idle/stalling problem last week. It turned out to be the fuel pump. When I replaced the pump the car did not start. Nor did I have any voltage to the pump or relay. I stuck a screwdriver in the afm and the car started and died. I reconnected the intake and the car started and is running great.
Your problem could be any of these things but chances are it's simple - air filter, clogged injectors, fuel filter, fuel pump or vacum leaks. Also, try pulling codes. Consult E30 net or Pelican as to the procedure.

[jillyjellyroll]

o2 sensors maybe, if you're feeling like it's going to stall and the car is running lean. have you had particularly sub-optimal gas mileage?

[omw41]

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[omw41]

"It's ECU, not ICU"...yeah...well I stand uncorrected. I hate it when people correct other people and don't know what they are talking about. I said ICU and I meant ICU. If you doubt the part exists and is located where I said it is...go to Pelican Parts and just type it in. Look at the picture so next time you know the differnce between an ICU and an ECU.

[NC318]

Thanks for the comments. It is not the plug mentioned by BBrg, as I checked it and it is tightly and apparently properly connected. And it's not the Idle Control Valve as that is less than three years old and has been cleared of any crap.

The fuel pump is an interesting possibility. I BELIEVE it has been replaced within the past three years. I will double check this. Is is possible that the fuel pump RELAY is defective? I have not noticed any real decline in gas mileage, and the defective relay would account for the idle issue, no?

I will also have them check the O2 sensors.

It is not the air filter as that is clean as a whistle, and is likewise not a vacuum leak as that has been tested and none exists (and should not, given that all the relevant hoses and the air mass boot are brand new replacements).

Like I said, vexatious.

[omw41]

Hmm...well if the relay was bad, I doubt that it would cause idle problems. I think that would cause bucking and the like...fuel delivery issues...but they are cheap enough, and if you're unsure, replace it...or Mike B. says he has good luck with cleaning the relay terminals. They say you can check the pump by turning the key over and going back and listening for it to click or hum or something like that, but I'm so old I don't hear that well. If you have a Bentley's Manual, go to the section on fuel delivery test and it will walk you through how to test your fuel delivery...it takes two people though..one has to just turn the key over...and the other measures the fuel amount. If you don't have a Bentley's, get one on amazon or something...I got a used one for around 30.00 with shipping. If you're anxious to do the fuel test...private message me and I'll spell it out for you...but I may not get to it for a day or two.

[NC318]

^ Thank you, I have walked through the section on this in Bentley's and will give it a shot.