1999 Pontiac Grand Prix Misfire Diagnosis from Computer Cod

ARMONDO

MEMBER
1999 PONTIAC GRAND PRIX
V8
2WD
AUTOMATIC
152,000 MILES

My check engine light currently goes off and on. One day while it was on, I went in to an Advanced Auto parts store and borrowed an engine code reader and it said that I have engine misfire. The Auto parts guy said that I need to change the spark plugs and everything should be okay. I should simply buy a service manual and read through it and it is very simple. The symptoms of my car is that I feel an engine vibration when I apply my brakes when driving down the highway. When pressing the accelerator everything is smooth. This usually occurs when I'm slowing down from a faster speed. I also get this vibration when driving at a slow speed at stop signs and red lights. Is this a good diagnosis from what I described?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

A tune up may take care of the problem as far as the vibration, but you have me confused with the vibration when slowing down. The engine isn't under a load at that point and you shouldn't feel anything. Where do you feel the vibration the most shen slowing, in the brake pedal or the seat of the car? I question if that is from warped rotors or drums.

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Monday, May 18th, 2009 AT 8:08 AM

ARMONDO

MEMBER
2 POSTS

I feel the vibration probably under the seat mostly. Sometimes there is a vibration simply when I'm going a little slow. I believe I've changed the brakes recently (6 mos or so).

-Thanks
Armondo

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Monday, May 18th, 2009 AT 9:17 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

If you feel it more from the seat, chances are the problem is in the rear. If it only happens when using the brakes, have the rear drums checked to see if they are out of round. Chances are they need cut.

Let me know what you find of if you have other questions.

Joe

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Monday, May 18th, 2009 AT 11:25 AM