1991 Grand Prix, Wet Plugs, Running rough

[Tim1052]

I've got a Grand Prix that has sat for awhile. It's running terrible, when you first fire it up, it will run smooth for 15 to 30 seconds, at around 1000rpm idle.... Then it tries to drop below that and starts to stall with out getting on the peddle.... Haven't even tried driving it, since its just almost fouling out.

Pulled the plugs, they are extremely wet. (this is a spare vehicle) battery went dead from sitting .... So I'm thinking it that flushed the memory out of the computer.... After charging it, and then starting it... It ran great for about 1 1/2 to 2 minutes.... Then it dropped right back into running rough... Seems as if one of the sensors is bad or something along the lines of the fuel injecting?

Thanks for any tips or suggestions.

[tblake]

Welcome Tim!

Does your GP have a 3100sfi or a 3.1mpfi motor in it?

If you have a 3100sfi, pull the vacuum line off the fuel pressure regulator and check for gas contamination. If you have the 3.1mpfi, you wont be able to get to the fpr.

Have you tried an idle re-learn after the battery became unhooked?

GM OBD1 Idle Relearn Process

[Tim1052]

Hey thanks for responding to my post, this is actually my brothers vehicle, which is sorta kinda going to become mine (alot of miles on it) sat for awhile, turning into a project to get running. I couldn't remember the engine it had in it.

This one actually has the 3.4l in it, I'm not sure how that differs from the 3.1l as far as fuel injection / mpfi.....

I will first try the idle relearn and see what that does for it..... The last time the battery died, it ran great at idle or 1-2 minutes... then started running rough again (seems as it warmed up)... So Let me try that idle relearn here in the next day (got alot of rain today) And I'll see what that does and go from there.

Searching the forums, were there quite a few problems with manifold leaks? Sounds like some of the rough engine posts, I saw some replies about checking for leaks around the manifolds.

I've got a really good retired mechanic that will look at it (I was just trying to maybe isolate the problem) and go from there with him...

Thanks again for the help and the welcome!

Tim

[tblake]

Yep, the 3.4DOHC, ahhh man!

As soon as you mentioned 3.4DOHC, I was thinking (intake gaskets).....

I dont know, you can try the can of carb spray and spray where the LIM meets the heads and listen for idle variations....

OBD1 Cars are so much for to diagnose. It helps when you can plug in your computer and it will display the data stream.

BTW, is the SES light on by chance?

[hopper1978]

i have 1990 Mc Laren model, had the idling rough problem, soon it filled with water. so i went and got the headgaskets and resealed the whole upper end. and yes it had to relearn. I'm sure yours isn't turbo charged. anyway have fun with it.