iac valve

what kind of symptoms come with a bad IAC?

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idling problems... vehicle won't idle after starting, or dies when coming to a stop.
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Tom Lawrence wrote:

Would that also cause the vehicle to hesitate when first started? I notice this more as the temp gets lower. I just start it and put it in gear and when I push on the gas, it will hesitate. Sometimes it backfires. Sometimes the engine even dies. Once going though, there is no hesitation.
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Not really... the sole purpose of the IAC motor is to allow the engine to get enough air when the throttle plates are closed (foot off the accelerator) to maintain proper idle speed. If the engine's idling fine, the IAC is working properly. It could be a bad TPS (throttle position sensor), who's job is to monitor the position of the throttle plates. The PCM uses this to say, "Ah hah, the throttle plates are opening, so I need to add more fuel, adjust the timing, all that fuel-injection stuff". The PCM uses the TPS reading as sort of an "early warning" that the mixture's going to go lean, rather than wait to sense a change in pressure within the manifold (via the MAP sensor).
Try this next time... put it in gear, give it a couple of seconds, then let off the brake, but don't give it any throttle. If the engine is still running smooth, VERY gently and VERY slowly apply some throttle. If that keeps the engine running good, but nailing the throttle from a stand-still causes it to hesitate, then I'd go ahead and troubleshoot the TPS with a voltmeter, and if found to be bad, replace it.
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Tom Lawrence wrote:

Thanks for the help. It gets worse the colder the outside temp. It doesn't do it much right now since its hot.
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