help with odd IAC behavior

[socal pat]

When I start the car dead cold in the morning it doesn't idle at 1100 and then slowly settle to 850 once warm like it used to. It instead starts right up and goes to 850 and stays there. Ok, not too big a deal. However, it now won't idle with the A/C on. Sitting still I can nurture the rpm's slowly down feathering the gas and it will idle with the A/C load, but blip the throttle or come to a stop in traffic and just release the gas pedal and it will just plain stall out.

With the A/C off it behaves just fine. I can be at 3500 rpm, push in the clutch and release the gas, and it will just fall straight to 850. No back and forth hunting. Sounds like a BRP hotside :shock:

So where do I look first?

[99mx5]

Did you perform the icle adjust procedure? I mention this because its very easy to overlook as the car will fire right up and idle fine after the install.

Warm the car up and then use the little blue allen wrench to adjust the throttle body to idle at around 850-900 RPM, then unplug the IAC valve connector, if the idle falls then readjust the idle again with the IAC valve unplugged so that the idle doesnt change when plugging or unpluggig the IAC valve.

Once you have the car idling around 850-900 with the IAC plugged and unplugged, drive the car as usual and do not readjust for around 2 days. This is so that the ECU can learn and adjust. After that period you may repeat the procedure to tweak the idle.

When done correctly, the car will idle fine when cold and the idle will rise when the A/C is on. The idle will also rise a bit when you turn the steering wheel.

Note: During the first day or so in the morning after the procedure the car may hesitate or stumble when cold, but the ECU will correct that.

[socal pat]

The idle was set by Mike's place after my initial install. This is a fairly new development. Maybe I'll perform the idle adjust again just to cover my butt then I'll get back to you if the problem still exists.

OH BTW I think I misplaced my idle adjust tool. Anyone know what size hex-head wrench it is? Thanks.

[Tom @ Fast Forward]

Sorry, I missed this post. I think it is a 3mm allen wrench.

If you develope idle problems where the car wants to stall, it is typically an indication of a vacuum leak.