1990 Coupe A/T Surging on Deceleration
Thread Starter
3rd Gear
Joined: Mar 2010
Posts: 3
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From: HIGHLANDS RANCH CO
1990 Coupe A/T Surging on Deceleration
I am a new guy and this is My first thread.. Need some advice, My car surges slightly on deceleration,mostly in overdrive,idles fine has good acceleration,does not miss. It has new: Injectors,throttle body,fuel pump, and regulator.86,000 miles and had a GM Trans @ 65,000. Local trans shop (trusted) said it might be Idle Control Valve?? It acts like it going in and out of lockup but not as severe.
Last edited by Mile Hi Charlie; Mar 17, 2010 at 01:08 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Not that your not feeling something, but without feeling it, difficult to give you a solution. The Idle Air Control Valve does act like a dashpot (when you let off of the gas) to keep it from stalling, but it's seamless (or should be) and capturing data with a Scan is the only way I know to see if it's being commanded to do that. Even if it is, it could be a bit sluggish if the throttle body is gummed up, so you might remove the Coupler from the Air Cleaner and look inside. If it looks like crap, taking it apart and cleaning everything may take care of what you're feeling. Otherwise, and you seem to mention this, it could be a torque convertor that's unlocking and relocking and since you had it at a trans shop they should have scanned it to see what that signal is. Did the put any info on a repair order for you?
Thread Starter
3rd Gear
Joined: Mar 2010
Posts: 3
Likes: 0
From: HIGHLANDS RANCH CO
1990 Coupe A/T Surging on Deceleration
Thanks for the reply! The surging is intermittant and it was doing it before I replaced the throttle body,about 3000 miles ago. The trans shop didn't put it on a scanner,but when I take it in for the front pump seal I'll have him do that. It starts right up has a smooth idle and accelerates great and shifts quick. If I do replace Idle Air Control Valve,should I try to find a GM part or aftermarket? Thanks Chuck
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I don't think it matters what you buy, but I've always used the GM (A/C Delco) part. If you do replace it, depress the accelerator slightly before and start it; let it run for 10 seconds; then off for 5 seconds and then restart normally.
Quick IAC test is to start it (helps if it's warmed up). Note RPMS. Turn it off and Restart. RPMS should be higher than what you noted, but return to that speed within a few seconds. If that's right, the IAC usually isn't a problem (and I've replaced more than one that wasn't bad).
I'd suggest you either obtain a Scanner or find some means to Data Log. Much easier to figure things out that way.
Quick IAC test is to start it (helps if it's warmed up). Note RPMS. Turn it off and Restart. RPMS should be higher than what you noted, but return to that speed within a few seconds. If that's right, the IAC usually isn't a problem (and I've replaced more than one that wasn't bad).
I'd suggest you either obtain a Scanner or find some means to Data Log. Much easier to figure things out that way.
