My 85 240 wagon has a nasty intermittent idle surge. When stopped, I need to keep my foot firmly placed on the brake in order to keep the car from taking off!

I have replaced the IAC and checked the hoses for leaks and have found nothing.

Any suggestions?

 

with the IAC unplugged, the idle should drop to 500rpm (in park or neutral, no A/C, fully warmed up engine).

clean the throttle body, and adjust the idle air bypass screw til it is doing 500 under above conditions, and make sure the idle switch is engaging (0 ohms at idle, open circuit anywhere above idle), then plug the IAC back in and it should idle at 700.

 

For the most part, she idles ok. Every once in a while, while I am stopped, if I don't have my foot firmly on the brake the car will try and take off. Also, have significant stumbling upon acceleration.

 

Clean the throttle body.

 

Resolution to the stumbling/hesitation on acceleration and idle surge-
Had to replace both alternator belts as they broke when alternator came loose.
Replaced alternator bushings and re-tightened everything. Also replaced distributor cap.

Both the hesitation and idle surge are gone!!!!!!!!!!!!!!!

If anyone has insight into this let me know?