2006 Grand Prix Running problem

kevnap65

Have a 06 GP, 3.8 car revs up and down then stalls upon starting. Throws a dtc of p0300 random misfire, anyone got any ideas?

Mr_Shiftright

Could be lots and lots of things.

Faulty spark plugs or damaged plug wires (examine plugs, test wires)
Faulty coil (pack) (no real test--examine for damage)
Faulty oxygen sensor(s) (test for proper output)
Faulty fuel injector(s) or erratic injector pulse (test with a NOID light)
Burned exhaust valve (compression test)
Faulty catalytic converter(s) (test by disconnecting)
Stuck/blocked/leaking EGR valve / passages (examine for damage, test operation)
Faulty camshaft position sensor (test output)
Defective computer or computer ground. (may require expert help).

imidazol97

Lots of things to check already listed by Mr.S.

Let me add

MAF. Cleaning with spray and camel artist brush may help. Replacement with an ACDelco is best test.

EGR. Already listed. Disconnect and run see if it helps. Remove carefully preserving the gasket. The pintel that closes the exhaust gases off can be cleaned with solvent but do not allow solvent to run upward into the control part at the top. I had an EGR where the sliding area for the pintel was sticking. I used gasoline and a plastic bristle brush from Harbor Freight to clean. Maybe even used a soft bronze bristle brush. Outdoors, of course. Don't do anything to generate a spark with your clothing and shoes rubbing other clothing articles making a static charge.

Timing chain worn? Over 250K miles? Not had good oil changes and quality oil through its life?

Air leak around the intake manifold, the upper plastic portion. Cracked? Warped? Try spraying carb cleaner around it as it's running to see if you get a change in engine sound or speed where it's being sucked into the air stream.

Also around the intake, check all the rubber vacuum hoses for dry rot and cracking. The closer to the engine they are the more likely to have hardened and cracked. Even pieces fallen away have happened. There's a hose on the front of the engine that goes to the control solenoid for the purge system. It has hard plastic tubes but in places has standard rubber parts.

This kind of uneven running or stalling after a start was a common symptom on Pontiac 3800s and Buicks when I was driving leSabres. I spent a lot of time reading the Bonneville forums for diagnoses as people worked through their problems. But I haven't been there for a while and don't recall all the causes found.

Best of all is if you have a friend with a similar year 3800 engine and you can swap the coils with the ones on that car and switch the spark control module UNDER the coils.

Good luck.

A search--if it's pontiacbonnevilleforums it's likely pretty good reading.

https://www.google.com/search?q=2006+pontiac+gp&rlz=1C1AOHY_enUS709US709&oq=2006+pontiac+gp&aqs=chrome..69i57j0l5.3110j0j7&sourceid=chrome&ie=UTF-8#q=pontiac+bonneville+idles+up+and+down+stalls&*

kevnap65

Thanks for the help, gonna try these things, oil changes were regular and the car actually has days in between where it runs strong, that's what has me stumped.

kevnap65

Oh yeah, got 174000 at this time

imidazol97

With good oil and regular changes, that's still low for problems with chain wear. Two of my leSabres made 200,000 mi, still running well. Not perfect by that time but running well.

imidazol97

You could have two separate problems. Fuel pump could be heating up and losing pressure. Have you driven the car with a fuel pressure tester duct taped to the windshield while it stalls?

Does it start right back up when it stalls? Crankshaft position sensors sometimes lose magnetism with heat and then when cooled will start up just fine. One test is to throw cold water on the CPS at the edge of the balance puller.

kevnap65

Ok, kool, thanks again, I'll post an update after I try these things

kevnap65

No on the fuel pump test, whether hot or cool, doesn't make a difference. Seems very random

kevnap65

And most times, yeah it starts back up

bigboy98

I was on the highway near my home and my car started stalling. It was about to shut off at a red light so i shifted it to neutral and gave it some gas to prevent it from stalling. Thankfully i made it home! The engine was extremely hot but at the same time the radiator fan wasn't turning on. The car kept misfiring and the tailpipe exhaust smelt like unburnt gasoline. And the check engine light came on - P0300 - random misfires. After 2 days of diagnosis such as spark plugs, spark plug wires, ignition coils, cleaning the electronic throttle body: the issue turned out to be the ICM (ignition control module or also called distributor) that is mounted right below the ignition coil packs. It's the most odd issue that car has ever given me and took me two days to figure out.

I was just adding this comment here so that if anyone else comes across similar symptoms, don't rule out the ICM. The junkyard sold me one for $30 that fixed up the issue! Diagnosing random misfires is sooooo hard! Check this out if anyone else comes across the issue: https://easyautodiagnostics.com/gm/3.8L/ignition-module-and-crank-sensor-test-1