Engine Performance problem
1999 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 145000 miles
I have a 99 GTP with 145k miles. When I was around 90k miles my car started to hesitate when I really punched the throttle. It didn't happen all of the time but enough to be somewhat annoying. My SES light started to come on occasionally and would stay on for several days before it turned off on it's own. After multiple trips to the dealer where they were more interested in selling me tires or replacing my belts instead of telling me what was causing the probelm, I have tried to replace parts that I thought may be causing the problem. The dealer's scan came back with codes P0300 and P0172. I don't remember which code shows the engine is running rich but I had already told the dealer, my MPG dropped from 29mpg to 19mpg. Now 55k miles later, I have gotten back up to 23mpg but the problem has got to the point that I'm nervous merging into highway traffic and I wouldn't dream of passing someone on the highway. It will happen in any gear but it does seem to happen a lot when right at the point of when it upshifts. I always have to get out of the fast lane when going up hill. I drive 100 miles round trip everyday to work and I either need to fix it or junk it. I can't take it any more!
Here is a quick break down of what I have replaced already:
(3) ignition coils
(1) ingintion module
(1) catalytic converter
Entire exhaust starting from behind Cat
O2 sensor (rear sensor by U-Bend)
all plugs (twice)
fuel filter (twice)
air filter (twice)
SC tensioner pulley
Fuel Pressure Regulator
Car has no MODS
I don't remember where in the time frame it happened, but my SC tensioner pulley had fallen off so I was driving for a while without any SC. It either happened right before I started having trouble or right after it started acting up. Could this have caused a problem? Right now it seems that the hesitation happens whenever the SC Boost kicks in.
Any help would be appreciated.
have the same problem?
Wednesday, May 27th, 2009 AT 6:39 PM