Just fired up my '93 after tackling the vac hoses....have 2 issues. Surging at idle (1700-2000), and while testing heater for coolant circulation, as soon as I turn the fan on high the rev's jump to 2500. Fan off-2000, fan on 2500. Any guesses as to what I've done? The car starts cold and runs smooth at 2000 for about one minute, then starts the hunting/surging thing.
Thanks,
Seann

 

Are you running a PFC? Have you done the idle learn procedure if you are?

-Geoff

 

Car is stock except for the exhaust

 

Hunting idle that high is usually a botched hose job/broken hose. You may have forgotten a nipple or misplaced a hose.

Make sure you connected all the sensors and ran the hoses right. Check your codes.

 

RE-RE-checking tonight.....vacuum related hunting idle makes sense, but never heard of a heater fan switch controlling rpm????????? Especially 500 rev's! That's the real head scratcher, any ideas?

 

lol I has having problems with my vacuum system so instead of redoing the one I had I cheated and bought one on forums that was already redone heh

 

I don't know anything about the stock ECU, but with the power fc ecu, electrical loads will increase the idle... the default setting is I think somewhere around 1000rpms for an electrical load with no ac. (normally, you bump up the idle only 100rpms for an electrical load from base setting, and 200 rpms for ac + electrical load from base settings)

I'm assuming the stock ECU does something similar to this, maybe with a vacuum leak this bump in idle is exaggerated.

 

At one point I had a ridiculous and mysteriously intermittent hunting idle(1500-2500). Turning on the lights would make it twice as bad.

A nipple on a vacuum line had torn. Replacing it completely eliminated the problem.