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2000 GP SE problems starting and idling

T

the daveman

New member
2000 Grand Prix SE. 3100 engine. 60,000 km. Two problems that may or may not be related.

One is rough idle especially when engine warm -- I think it's running lean. Rough idle is worse in Park or Neutral than in Drive. When on level ground in Drive, removing foot from the brake pedal results in surging while the car moves forward very slowly, but when pressing the accelerator the engine smooths out. Occasionally when stopped at a light, and the engine is first warming up after running for 3-5 minutes, the engine will bounce around and the whole car will shake for about 5 seconds while the RPMs jump around. Then it stabilizes.

No warning lights displayed on dash. Dealer has scanned for codes more than once but none found.

2nd problem is difficulty starting the engine. More often happens when engine is warm. Engine will start but then immediately stall. If I hold the key in the "start" position, it'll usually start after the 2nd "try" i.e RPM will drop really low after the initial start attempt, then it cranks some more and starts successfully. This has been getting gradually worse over time. But about half the time the engine starts perfectly on the first try with no problems -- RPMs stay up and slowly drop to idle level.

Tried the following already: Replaced fuel filter -- seemed to smooth out the idle for a short time only. Replaced spark plugs. Replaced PCV valve. Replaced battery. Fuel system cleaned by the dealer. Transmission flushed by dealer.

Any suggestions would be appreciated!
 


I would think for your first problem it could be your engine mounts, but I am not postive because it only happens when you are idle. For your second problem, i have no ideas. :)
 
Well I've cleaned the throttle body and that fixed the difficulty with starting the engine! (found a reference to this on a different forum on this site). There were some deposits in the throttle body, maybe just enough to impede air flow or cause a sticky throttle plate. It's all clean now.

The rough idle continues. It's not severe, but just bad enough to be annoying. Thanks for the engine mount suggestion -- no problems found with the mounts that I can easily see.

My next steps are to clean the idle air control valve and/or the mass air flow sensor.

The IAC might be a bit tricky to remove -- the fuel lines are close by and I'll have to route the screwdriver around and under them. I'll post again when I get that done.

And as before, any suggestions are appreciated!
 
If the IAC doesn't cure it, check your plug wires, and have your ignition coils and ignition control module tested (they're very easy to remove, and most parts places will test for free). Even better, swap them out if you have access to spare coils, as some coils have tested fine many times even though they're on their last leg. Also, get a reading on what kind of voltage your charging system is putting out. This almost sounds like there isn't enough volts for everything to run properly.
 
I'm still working on the IAC valve. Anyone know how to remove it?

There are 2 screws, but too many other components nearby for me to get my driver or socket wrench to the screw that is closest to the engine. The main problem is a plastic assembly that contains hoses and electrical connections; it's located right behind the electrical connector for the IAC. I was hoping that assembly pulls upward and off the metal mount somehow, but no luck yet.

A new IAC valve isn't too expensive, so I've ordered a new one. But I was hoping to install it myself rather than pay the shop to do it.

Thanks again.
 


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