surging idle

[dmann1]

I'm working on 99 camry 2.2l it has a slight idle surge when warm. not bad maybe 200-300 rpms surge worse with a/c on but will do with a/c off. I replaced the iac under the t-body. and clean the throttle plate. no codes system passes. no pending codes. seems to run just great other than the surging. I've check for vac leaks and there doesn't seem to be any. Any suggestion would be great thanks for your time

[AlmightyCamry777]

one possible cause, often it IS a vacuum leak. sometimes caused by worn out power brake booster (it is operated by engine vacuum). A check of the hoses and for other kinds of vacuum leaks might not uncover this.
Does it surge with engine hot, cold or both? If the engine temperature doesnt matter, then it may still be a vacuum leak.

[Mike Gerber]

After checking for vacuum leaks, check the engine coolant temperature sensor for being out of range; check it both cold and hot.

Mike

[fenixus]

double check and then triple check for vacuum leaks. they are usually a bitch to find (unless they are obvious which happens rarely). here are some helpful hints on finding the source of vacuum leaks:
http://www.aa1car.com/library/vacleak.htm

also make sure your wiring harness grounds under hood are good, if one of them is bad (and e.g. reacts to temperature) it may cause the electrical sensors and motors to go a little crazy.

most important ones on your 5s-fe are:

a) on the back of intake manifold, passenger side, bottom - this one seems to ground all ECU circuits including most sensors

b) behind both headlights - some sensors might be grounded to them

c) on both radiator support braces (bumper may need to go off to access them) - less important grounds

there is more grounds in cabin (7 around dash area), behind kick and cowl panels on both sides and at the center console (both sides), pay attention to those especially if your car has some aftermarket equipment using those grounds.

refer to Electrical Wiring Diagrams for more help with electrical systems and grounds:
http://www.camrystuff.com/index.php?page=Gen4_Manuals

[Stillrunning]

Bad injector o-ring will also cause vac leak. Also check PCV area hoses. I don't know whether a faulty A/C idle-up signal will cause this. More than likely it's a vac leak. When on A/C and the engine rpm adjusts up is the surge above this up'd idle or does it fluctuate lower then higher to A/C proper idle giving "surge" simulation?

[rustynut55]

I too have a surge at idle. But only on warm restart. No surge if I restart within about 5 minutes or so but if the engine cools for about 10 or 15 minutes I get a 300 rpm surge at a frequency of every 2 or 3 seconds. If I blip the throttle or just leave it alone for a minute, the idle smoothes out at 650 rpm. I recently changed both O2 sensors because of a check engine light. The O2 sensors fixed that but made no difference in the surge symptoms. I also cleaned the throttle body with throttle body cleaner, a rag and a toothbrush. No sticking of the throttle plate. Did not take the IAC off but let the cleaner soak into the IAC air channel. That did not make any difference either. I will check closely for vacuum leaks this weekend. This hasn't had any effect on drivability but it is very curious.

[BamZipPow]

Originally Posted by rustynut55

I too have a surge at idle. But only on warm restart. No surge if I restart within about 5 minutes or so but if the engine cools for about 10 or 15 minutes I get a 300 rpm surge at a frequency of every 2 or 3 seconds. If I blip the throttle or just leave it alone for a minute, the idle smoothes out at 650 rpm. I recently changed both O2 sensors because of a check engine light. The O2 sensors fixed that but made no difference in the surge symptoms. I also cleaned the throttle body with throttle body cleaner, a rag and a toothbrush. No sticking of the throttle plate. Did not take the IAC off but let the cleaner soak into the IAC air channel. That did not make any difference either. I will check closely for vacuum leaks this weekend. This hasn't had any effect on drivability but it is very curious.

You could've easily damaged yer TPS as the throttle body cleaner can dork it up. Best thing is to put a computer diagnostic on the car and see what the signals are. Current pricing on AutoTap Express DIY is $50...well worth the price!

[rustynut55]

Yea thanks. I think the air control is ok as when cold or hot the idle is stable and correct. Havn't found vacuum leak yet. Really like your idea of some kind of control system reader. I just have one that reads check engine codes. A friend at work is a German car nut and he was telling us about this reader he bought from VW that allows him access to all the computer streams in the car. He can change his fan speed, control his radio and even bleed his brakes using this reader and the cars computer. Don't know who makes it or what it cost but sounds like fun!