after warm-up my 91 GT idles at 1200-1500 rpm. This usually happens after 15-30 minutes of driving. When it first warms up idle is normal. anyone with any ideas? 112,000 miles on the car, and other than this the car runs fine.
well the bypass air valve is the thing that makes your idle higher when you first start the car up. This valve is open and shut by temperature variations and is in no way connected with the electrical workings of the ECU. I´s suggest taking the BAV (bypass air valve) out and then replacing it and that should fix the problem. Also check the idle speed and make sure that the throttle flapper isn´t stuck open.
Thanks for your suggestion, I also had thought of that. What I don´t understand is that it will idle fine after warm-up and for 10-15 miles after that. If I drive more than about 15 miles after it is warmed up it will kick the idle up 500-800 rpm. It doesn´t seem to matter if I´m on an open road or in stop and go type traffic. Also I´ve found that if I turn on my ac after the idle jumps up it drops back down to normal idle. Turn it off and it jumps back up to 1200-1500 rpm.