Ford Repair: 1995 Taurus 3.0 L low idle speed, vacuum leaks, light flickers

Question
I recently purchased a 1995 Taurus 3.0 L with 65000 miles. It runs great when you start it, after about 30 minutes the idle speed decreases when you come to a stop and still in gear. There is a small amount of vibration and the oil light flickers. If put in neutral the idle speed increases enough that the flickering stops. It also increases if I turn off the A/C. If I stop the engine for even a few minutes it will run fine again for about 30 minutes. I know the car overheated before I purchased it and the head gasket was replaced. Other than that I do not know its history.

Answer
Sounds like an idle control valve issue. Either it is dirty and sticking, or just doesn't work. This valve is on top of the throttle body, with a two wire connector. With the engine running, if you disconnect this valve the engine should stall or drop in rpm. If it doesn't the valve may be stuck. You could clean it with carb cleaner, but may be better off with a new one.

When you put the car in gear or turn on the ac, the idle valve should adjust the rpm for the added load. If you do have to replace this valve, disconnect the battery for 5 minutes to clear the learned strategy, then run the engine at idle for five minutes to help relearn the idle speed. It will take some driving to get the PCM relearned completely.

Also check for vacuum leaks. This engine is prone to failure of the vacuum hose from the EVAP system to the PCV line.