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Tractor Talk Discussion Forum

OT, Pontiac Bonneville

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Mattchew

09-07-2004 18:12:04




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Guys, See some car questions on here and got one myself..maybe you all can help...
WHen my car (GM V6 - 3800 engine) is hot after driving 30 minutes, etc. I turn it off, 5-10 minutes later when I restart the car, it runs rough....almost like it will stall...the engine seems to rev up and down, if you come to a stop light and it's doing this, it will continue while you sit at the light...after less than 1 minute of this, it goes away...it will also go away if you put in park and rev up lightly with the pedal...
Only does this when it's hot...this is the awesome GM 3800 engine....173,000 miles and going strong....is this a coil or ignition problem?
THanks, Matt

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Chris Vangel

09-09-2004 04:30:30




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 Re: OT, Pontiac Bonneville in reply to Mattchew, 09-07-2004 18:12:04  
Another item to check is the throttle plate. Although you didn't state the year, these engines had Mass Airflow Sensors. If the throttle plate gets coked up, the engine will run poorly at idle, if not stall, but normally runs fine at speed. I clean the throttle plate with carb spray and an old toothbrush. This can cure a lot of rough idle stall complaints. The mass airflow must be clean also to get the proper reading, however it is delecate and should be taken care of by a tech if your not sure about cleaning it yourself. I usually use a q-tip soaked with brake clean because is will not leave a residue. good luck.

Chris.

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Allan in NE

09-09-2004 04:55:22




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 Re: OT, Pontiac Bonneville in reply to Chris Vangel, 09-09-2004 04:30:30  
Hi Chris,

Good call on that one. I'd forgot all about that throttle plate and how they carbon up in behind.

I used to use that alcohol based brake cleaner and it would bring 'em right out of it. Trouble is, they discontinued that cleaner. :>)

Later,

Allan



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Jwh

09-08-2004 19:12:30




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 Re: OT, Pontiac Bonneville in reply to Mattchew, 09-07-2004 18:12:04  
The first thing I'd check is for gas in the vacumn hose of the fuel pressure regulator. If the hose is wet, replace regulator. Jim



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Allan in NE

09-08-2004 03:42:34




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 Re: OT, Pontiac Bonneville in reply to Mattchew, 09-07-2004 18:12:04  
Mornin' Matt,

It is just about impossible to diagnose that old gal "over the phone". Are you getting a 'check engine' light?

Are your fuel and air filters in good shape?

Could be a faulty fuel pump, wobbled out Idle Air Control, worn TP switch, wobbled out injectors, who knows?

You don't use ethanol do you? The early ones could not stand up to ethanol use and cost many an owner a set of injectors.

Could be a bad ignition switch, ignition module, a bad temp switch to the ECM or even the ECM itself.

Could even be defective O2 sensors or their heaters.

They don't use a single coil; and depending on the year, they use what they call a "coil pack" (3 coils in one unit), which is fired by the ignition module. The newer ones use a different coil for each plug and totally eliminate the plug wires.

Or, it might even be a simple thing like just needing a set of plugs.

The last one that I worked on that was doing what you describe, came from over in Wyoming and reached me after the owner had sent it to every garage he could think of to get it repaired.

That one ended up having the wrong ECM, which was calibrated for California, installed somewhere along the line.

Your best bet is to take it to someone who can plug 'er in to a scanner and read the numbers and see what is going on with that guy.

Hope ya get ‘er goin’,

Allan

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Richard

09-08-2004 14:55:26




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 Re: OT, Pontiac Bonneville in reply to Allan in NE, 09-08-2004 03:42:34  
Don't forget a stuck open pcv valve. they rarely ever get changed on those engines and could cause a vacuum leak that the Idle Air Control Valve is trying to compensate for. My 2 cents from an ASE Master...Good Luck



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Old Pokey

09-07-2004 20:55:27




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 Re: OT, Pontiac Bonneville in reply to Mattchew, 09-07-2004 18:12:04  
Sounds more like a fuel problem. When you shut it of hot, the fuel around the engine gets hot to. It is almost on the verge of turning to vapor. When it does turn to vapor in the line it causes what is called "vapor lock". To do more troubleshooting, next time you shut it off hot, open the hood and laeave it open so the hot air can escape. Then see if it still does it 10 minutes later when you start it. You might also try a can of fuel stableizer. Its also possible that it can be as simple as a fuel filter or even a fuel pump that is on its way out. Another thing to check is any tin sheilds around fuel lines that are missing. If its got that many miles on it, sometimes the fuel line itself can start to degrade and cause unusual intermittent problems.

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