formula31

Last week my 1991 Grand Prix started stalling everytime you take your foot off the gas pedal, no matter what temp or speed. It runs great as long as you keep a little pressure on the pedal. I took it to the dealer yesterday and of course it ran great for them, no fault codes, nothing, no problems. So I took it home last night and sure enough, it started stalling again. I dealer wants to start replacing parts and I dont want to put a lot of money in the car for troubleshooting. Anybody have any ideas what this could be? I only want to get a couple more months out of the car.

Gary Anderson

I've never worked on a pontiac 3.1, but I'll take a shot.
If it stalls in gear or park, it may be the IAC (idle air controler). If it only stalls in gear when coming to a stop, it may be the TCC (torque converter clutch).
Gary

formula31

Thanks Gary, Thats a start. It stalls in both conditions. Where is the the idle air controller? What does it look like. Sorry about the dumbness but I am totally a carb man. It does act like there is no dash pot or idle stop screw, but only sometimes. Does that help any more?
Tom

Gary Anderson

If it's a 91, I'm guessing it has a throttle body FI. Look around the base of the throttle body on the manifold for a box with a couple wires coming out of it. It should unscrew from the manifold. This has a servo in it that screws in and out to control idle speed when your not on the gas. It may or may not send a code if it's bad, or it may just be carboned up. Most GM units are cheap, about $30, so you might just want to replace it.
Might be a good idea to consult a manual. Most librarys will have one.
I'm kind of guessing on this, I've mostly worked on SBC motors.
Good luck,
Gary

Mrgoodwrench

Is the transmission a 3 or 4 speed? Was the battery dissconnected or replaced recently?

merlin540

if the battery was disconnected the computer will have to learn how to control the idle .also see it the throttle plate is carboned up this can also cause the problems that you are having because of the engine not having enough air pass the throttle plate to have a base idle setting

formula31

It does have a throttle body and I will check for carbon. I believe it is a 4 speed auto but not sure. I know about the program loss, This car will not retain its memory. I did have the drivers door window drive motor replaced recently at a dealer but the car ran fine for a few days after that before this started. Good suggestions, Ill start on them when I get home tonight. The dealer wanted to: replace the injectors, rebuild the throttle body, replace the fuel filters and maybe pump, etc. The car runs great and gets 30 mpg on the highway. It does sound like this IAC think might be sticking or intermittant.

Thanks. Sounds like I have a place to start. Can I clean the throttle body in place and if so, with what? Carb cleaner? Engine running or not?

merlin540

not running and use carb stray with a small brush to clean carbon we do it all the time and it does work

formula31

Ok heres a pic of what I am looking at. While it was idling OK (go figure) I disconnected the thing on the right that looks like it has a couple solenoids-no effect. Then I disconnected the thing on the left-no effect either. Then I disconnected another thing on the left under the other thing and the idle sped up. Hooked everything back up and cleaned out the throttle body and now it idles like ****. Im gonna take it out and run it to see if it straightens out.

GO4BROKE

iTrader: (1)

Its been a while but I used to be a Chevy tech. The first thing you should do is remove the rubber bellows between the air cleaner and the throttle body, use carb cleaner and a rag to clean the throttle bore, make sure to clean the edges of the throttle plate and the bore around the plate. This will restore the minimum air rate(the gap between the throttle plate and the bore). Next remove the IAC (the thing on the left of the throttle body when looking from the drivers side), 2 torx bit screws retain it, and clean its pintle and its bore, re-install it. Next remove the EGR valve(the ting to the right of the throttle body, has 3 solenoids mounted together) and clean the 3 pintles, making sure they aren't sticking open or closed, reinstall it. Now disconnect the battery cables and touch them together for 1 minute to make the ECM forget everything. Hook the cables up, set the e brake(Careful with this step please!!!), block the wheels, start the car and put it in gear. Let it idle in gear for 15 minutes. 90% of the time this will fix the stalling. If the condition persists, the first parts I would throw at it if you can't find someone to properly diagnose it for you would be an EGR and a coolant temp sensor. Good Luck!!