Anyone have an idle control valve go bad?

[T86951]

Has anyone have an idle control valve go bad? What did it do? How was it different when replaced?

Thanks

[e_nough]

what are the symptoms?

[T86951]

Car starts great, no flooding at startup but the rpm's are about 700 and gets rich in just a couple seconds and puffs a little back smoke, in about 30 sec's it clears out and idles normal and smooth and runs great. The colder the weather the worse it is. In the summer at 80-90 degrees no problem. I read that the idle control valve puts more air in the engine on cold start to mix with the larger amount of gas the injectors put in when cold so the car will idle up until it warms up. I have gone thu my injectors and it is not flooding at startup. Starts real fast and easy soon as I hit the key. it is my na '86 daily driver.

[Magnus_944]

I don't think your problem is the cold start valve, I'm not 100% sure, but this is how I think the system works and why I don't think your problem is the cold start valve..

If the idle control valve is bad and don't open to let more air pass to raise idle the system will not add more fuel. All air the engine consumes passes the air flow meter which sends info to the DME and the DME determines how much fuel it will inject to give the right mixture. If the cold start valve don't open no extra air will pass through the cold start valve, and no extra air will pass through the air flow meter, and the DME will not add more fuel. http://Studentserv.itn.liu.se/~magka158/temp/system.gif

Does anyone know that this is not right? Please tell me, I like to learn more

/Magnus

[1.2gees]

Magnus_944

What you're saying is not really wrong, however it might lead you to think a little off.

Let me explain:

When the engine is cold (and the DME could only know through the engine temp sensor), it's supposed to run richer. Richer, EVEN THOUGH the aux air valve gives more air.

The air that the aux air valve draws does go through the MAF sensor, but it does NOT go through the throttle plate, so the throttle position sensor doesn't know that the engine is getting more air. (BUT the DME does, it is afterall monitoring the engine temp. sensor, the air flow meter, throttle position sensor, as well as ignition/crank timing among others, in short all engine parameters. The aux air valve is also controlled by the DME). Anyway, the point is, the car's supposed to run richer than normal, when cold. If the aux air valve doesn't open, it'll still run rich, even richer than it should while warm.

In a perfect world, what you say is true, the DME would know that only so much air is going into the engine, but the "Barn Door" air flow meters aren't that precise.

I'm willing to bet that a properly installed "hot wire" air flow meter alone would help this problem big time, not that that's the source of it.

I hope this helps a tad,
Ahmet

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It's all the driver...

[nigel]

I too believe that my idle control valve is shot. The engine runs perfect when hot, but here in England our cold winters make the car stall as soon as I pull up at a set of lights or something. It seems to clear once the engine is warm. On the subject of black smoke, I once had a guy in a car behind me pull up along side, to tell me that my car was smoking, this was within a mile of home. I know for sure there's no smoke when warm..........so it looks like a new valve is required!

[1.2gees]

Nigel, yours might be bad valve seals...

Aux air valve will NOT make your car smoke excessively, it'll just run A TAD richer that's all...

If your car's running rough, mixture might be off, if it's smoking bad enough for someone to tell you, it aint an incorrect mixture!

Good luck with it though, and keep in mind, if your car burns oil, DO NOT use synthetics.
Ahmet

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It's all the driver...