Engine Idling High (My best description)


I have a 1998 Toyota Avalon XLS; bought used in 2000 with 45000 miles. Moslty in warm/hot climate.

Drives smooth and quiet on the highway, except for recently when I accelerate above 75 mph and sustain that speed for at least half hour. When I stop, the car appears to idle very high until it cools down. No warning lights are coming on and it gets an old change at least every 3000 miles. The dealership has taken almost $2000 to fix the problem- and after 2 visits- I have given up and the problem has not been fixed.

Any idea why this might happen only when the car travels 75 mph and beyond? Thanks, I will watch for a response.

The heat from running the engine at higher power outputs, may be causing the intake manifold to open along the manifold-to-head margin. Check this by running it in that manner, then, play an unlit propane torch around that margin. The intake manifold may have a crack which opens when the engine gets hot. If the idle increases, you’ve found the vacuum leak.
Try another thing to isolate the problem: pull the electrical connector from the idle air control valve when the engine races. Note effect. Click on this for picture of iac valve http://www.autozone.com/N,15900207/shopping/partTypeResultSet.htm