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IAC Issues
Oh it feels good to be back on the forum I haven't had many issues with the car lately until now. I think my IAC is going bad. When I turn the key to the position that turns the fuel pump on(right before starting the engine)shouldn't the IAC retract and let air into the throttle body? I'm asking this because I've had problems with idle at start up, and sometimes during driving when I take my foot off of the gas to apply the brake, the car stalls.
I read online that the IAC should retract when the key is turned to the second position, right before the car is started. Am I right or wrong? |
This is for my 97 Bonneville from AllData....
The purpose of the Idle Air Control (IAC) valve is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. By moving a conical valve, known as a pintle, in (to decrease air flow) or out (to increase air flow), a controlled amount of air can move around the throttle plate. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM. The IAC pintle moves in small steps called counts. During idle, the proper position of the AC pintle is calculated by the PCM based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls. If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the key is cycled ON then OFF. When servicing the IAC, it should only be disconnected or connected with the ignition OFF in order to keep from having to reset the IAC. The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is open fully, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. DTC P0507 may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with possible hard starting and a rich air/fuel ratio. DTC P0506 may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load. |
For years I have had decent to bad idle that would come and go. Then one night the car stalled, but started back up with no problem, this happened about ten times in the last 9 months. Also when the car was in drive and at a complete stop the idle would get really bad and drop to about 700 rpms. And when I would start the engine cold it was really loud on start up for about the first 60 seconds or so. Tonight I installed a new IAC and it's like I'm driving an new car, all of the idle symptoms are gone and the car is much quieter on start up. And I noticed that my aftermarket stereo is getting more amperage do to the higher rpms at idle. My car is a 98 Bonneville, if you have the original IAC in your car I would change it, you can thank me later.
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Glad you found/fixed the problem.
Thanks for updating us. |
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