Weird Idle Surge Problem

[AG 305]

Im Having A Very Strange Idle Surge Problem And Im Hoping You Guys Can Help Me Out. The Car Is A 91 GSX And It Is Completly Stock!

Heres The Problem:

The Car Only Idle Surges At Initial Startup When The Motor Is Cold. Car Revs To 2k Then Starts To Surge To 1.8k Then Back Up To 2k. I Watch The Temp. Gauge And As The Car Warms Up The Surge Begins To Drop From 2k To 1.8k Then Up To 1.9 Then Down To 1.7 And So On All The Way Till It Stays At 1k Where I Have The Idle Set At. The Problem Completly Goes Away Once The Temp. Gauge Reaches The 1st Little Line. What Can It Be?

HAS ANYONE EVER HEARD OF OR SEEN ANYTHING LIKE THIS?? OR HAD IT HAPPEN TO THEM??

PLEASE HELP!!

 

[ptownracer]

have u tried cleaning the IAC idle are control valve? mine did this after i installed the cams cleaned it and it fixed the problem i had severe carbon build up at 90,000 miles

 

[Lofty]

This is pretty normal.

It's supposed to idle high because it has electronic choke control, it auto revs the engine to help it warm up faster.

It should drop down when it hits normal operating temperature.

Check the resistances between the pins on your ISC.
Go to VFAQ.com to learn how to do that.
Other than that it seems pretty normal.
Also a good cleaning doesn't hurt either, the stepper motor is jamming on carbon so that would cause irradic surging.

 

[91AWDGSX1G]

AG 305, I am having the same exact problem. I bought a new ISC. Took the throttle body apart and cleaned it (replacing FIAV, shaft seals, and both throttle body gaskets. My car will actually hit about 1.8K for one to two minutes and stay there. Then it will surge until operating temp. I will keep you posted if I fix it. My vacuum is at 12 hg, told that is low. Will check for boost leaks. What is your vacuum reading???? Before I did all this my SAFC II was sitting at -30 (which is super rich but it didnt have any problems (bought it like that). I have adjusted the SAFC II to 100% LFT and it started doing this. Well good luck.

 

[AG 305]

I Found The Problem. Turns Out I Had A Gigantic Vacuum Leak. I Removed All My Emissions Stuff And Blocked My EGR. Its Fixed Now And Everythings Perfect.

 

[Steve91]

im having a similar problem, when i start the car cold it idles to 2100 and as it warms up it surges back and forth untill its warmed up and stops. im also getting very little vaccum as well...plllease help!