My son's 90 4Runner with a 3.0 V6 has a strange problem that comes and goes. We rebuilt the engine about a year ago and since then this idle problem comes and goes. If you have the AC off and your foot off the brake it idles at 700 RPM steadily. When you press and hold the brake, the engine idle will start oscilating beteen 1200 and 500 RPM almost stalling at times. As soon as you take your foot off the brake the idle smooths back out at 700 again.

It may idle properly for a month and then this problem comes back for a few weeks. We haven't seen any pattern to the timing of the problem.

Sounds like some kind of vacume problem that's tied to the brake system but you got me. I have looked for vacume leaks and loose vacume lines but I haven't found anything yet. Anyone have any ideas?? Thanks.

 

Nevermind. I did a search and found that if the idle is set above 1000 RPM then the ECU controls will cause this problem. I set the idle back down to about 700 and we'll keep an eye on it.