Help with stalling in a grand prix

Hello, i am writing this for a friend of mine. He has tried to figure out what causes the "stalling/bucking" in his car through several persons and mechanics, but no one can figure it out. Most can't even reproduce the problem when they drive the car.

Car Info: 1993 pontiac grand prix le 3.1 L v6

The Problem:

When the car is moving at low speeds (about less than 30 MPH) it "tries to stall" or just turns off if stopped. This doesn't happen every time the car stops. When it "tries to stall," its like its going to, sputters and either turns off or keeps going and the "sputtering" goes away.

At higher speeds (highway speeds of 50-70 MPH) the car also sputters, but it bucks really hard. Like if you were on a horse! It almost sounds and feels like someone crashed into the car! After a few seconds of this, it stops ("goes away").

When bucking, rpm needle fluctuates about 500 rpm in both directions (up and down, more or less)

Additionally, the driver has noted that when the car is left sitting over night, he can get about 15 mins "more" out of the car before the problems start again. Normally, the problems start anywhere from a few mins to 15-20 mins. So at best, he may be able to go maybe 45 mins before the first problem from parking the car over night.

What the driver does:

When either of the above happens, he has tried to let off of the gas, but the problem continues. He has tried to "floor the gas pedal" and the problem continues. He has tried to pump the gas pedal, and the problem continues.

Things he's done to try to fix the problem:

changed: gas filter transmission oil pan changed (needed replacement anyways) transmission oil changed spark plugs air filter engine oil change

run diagnostic on motor and transmission - all clear, according to the technicians running the tests.

changed gasoline type from 87 octane to 91

As of this writing tried a fuel injector/valve cleaner additive through the fuel system. (with maybe 1/4 of the tank usage, he has noted "maybe slight improvement.")

Originally when this problem began, it was winter time of 2005. He stopped using the car because he thought it was the transmission, and instead borrowed a truck. When he took it in to have the tranny checked out, it checked out fine. So he tried driving it again, and it continued to have the same problems. He then did the small item replacements and nothing helped. He says he maybe within the last year or two replace the spark plug wires/cables.

Now in june of 2006, he's trying to fix the car because he has a break from school. So he and I as well as others have been trying to figure it out, but we don't know what else it can be. I think possibly heat could be a cause of the problem. The driver also read that a MAF (Mass Air Filter sensor?) could be a/the problem.

So, here we are asking you guys for help! I have pictures of the engine compartment if you think it could help at all. And if you have any suggestions of things we could modify ourselves, please let us know.

Ok we wait your replies. Thanks again.

Reply to
Mr Hanky Poo
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Reply to
Shep

Sounds almost word for word as to how mine was acting. It was the MAF or MAS (depends on the make what it's called) It was around 500 bucks or so on my

Reply to
Jim Northey

Thanks for the quick replies guys. I called my friend up and repeated what you guys said. He is going to see if he can come up with a fuel pressure gage, and look into replacing/fixing the maf/mas. He's a college student so funds are kinda limited, so it may take some time. But as soon as he does anything i'll let everyone know.

Reply to
Mr Hanky Poo

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