1988 Pontiac Grand Prix Stumbles When Warm

1988 PONTIAC GRAND PRIX
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GREEKGUY7
  • MEMBER
  • 7 POSTS
I have an '88 Pontiac Grand Prix with a 2.8litre V6 and auto trans. The car starts well, idles ok and runs ok when cold. Once it warms up and I try to accelerate normally from say 20MPH to 30MPH the car would stumlbe badly to the point that if I dont let off the accelerator it will stall out and die. It will restart immediately though. If I immediately let off the gas, it will keep running.

I replaced the TPS sensor and adjusted it for .55V at idle, and did idle relearn a couple times. The plugs, wires, filters, etc. have been changed in the last 10k miles. No codes either. The car has not been driven regularly for the past year partly cause it would do this sometimes, and partly cause it would die at idle in the past sometimes. The gas is new as I have been trying to get it to run right for the past few weeks. Any ideas or suggestions?? THANKS!! :cry:
Mar 7, 2006 at 2:58 AM
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RUGRUV
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  • 45 POSTS
No codes.. hhmm...

I would start with the easier stuff like impurritites in the fuel system or clogged filter even if it was changed only 10k ago. Have a look at the sparkplugs for foulling and proper gap. And look for a vacuum leak around the intake manifold.

If these don't help.. then ignition timing and how the fuel is getting into the engine. Look for signs of white carbon on either ends of the plug wires and the distributor and solenoid wires. Perhaps cracks in the distributor too.. This might elliminate anything really obvious.
Mar 7, 2006 at 7:01 AM
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NOS
  • ✓Experienced Mechanic
  • 320 POSTS
does this car ping by chance? or spark knock the computer may be trying to over compensate this wil cause stumbling a stuck open EGR valve with carbon stuck under the pintle will cause this also will also cause rough idle. bad fireing plug,wires,etc will also cause all this stuff. don't put injector cleaner in your tank let a pro clean them through the fuel rail. also if you live in a cool climate use heat in your gas water in fuel will also cause stumbling.and if it has been setting awhile water is heaver than gas and will settle to the bottom of the tank and will be the first to be picked up by the pump.hope this helps (NOS)
Mar 8, 2006 at 3:29 PM
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Suggested Repair

Check for spark knock that may make the computer overcompensate, and inspect the EGR valve for carbon holding the pintle open. Also check plugs, wires, and the distributor for fouling, cracks, or carbon tracking; look for intake vacuum leaks, a restricted fuel filter or fuel contamination, and water in the tank from sitting. Have the injectors cleaned professionally through the fuel rail rather than adding tank cleaner.

Conversation Summary

An 1988 Pontiac Grand Prix 2.8L starts and idles fine when cold but stumbles and can stall on light acceleration once warm, then restarts immediately. The TPS was replaced and set, recent tune-up parts were installed, and there are no codes. Replies suggest checking fuel contamination or a clogged filter, plug condition and gap, intake vacuum leaks, ignition timing and distributor condition, spark knock, a stuck-open EGR valve, and water in fuel from the car sitting. Professional fuel-rail injector cleaning was advised instead of tank additive.

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