Pontiac Repair: 2003 GT unsolved issues, advanced auto parts, grand prix gt

Question
QUESTION: My 2003 Grand Prix GT has been having some issues that 2 garages/technicians cannot seem to figure out. I was first informed my car had a misfire code #6 therefore, to help resolves the issue or hope that it would I have replaced with new...all spark plugs, wiring, coil pack, fuel injector and I was told that the motor runs very good and it's strong but, only issue the car has now is that when driving it stumbles/hesitates. I also had the sensors changed as well. Could you please help me determine what you think I may have not tried doing or have not replaced that could possibly be causing the car to have hesitation?

ANSWER: Hi Lisa:

do you know if this is setting any codes now? stop by one of the big box auto parts stores and hive is scanned for codes and see what may be stored in the computers memory that will help. Hesitations can be cause by a lot of things. what engine is in this? does it hesitate from a stop or does it hesitate when your driving and accelerate when it does it? When was the last time the fuel filter was replaced. You can try a fuel additive calle Chevron Techron you can get that at Wal*mart follow the directions on the bottle. I have not found another product on the market that works as well as that does.

---------- FOLLOW-UP ----------

QUESTION: Not sure about any new codes because my car is still at a garage being looked at right now. Last thing I was informed is that the technician was going to pull the engine head off to see if maybe it's a vaccuum leak or something of that nature because he informed me all else looked good, just can't figure out why the hesitation. Hesitation occurs most when I am sitting still otherwise the car drives smoothly.Not sure what the name of the product is but, I did try a fuel additive that was purchased at Advanced Auto Parts store roughly a month or so ago and it helped ease the hesitation just for a short time and then it returned. When I am sitting at a light or at a stop I litterally feel as if I am getting a whole body massage from the way this car hesitates, its pretty rough at this point. Not sure with the fuel filter because I has last year a K&N thingy placed into the car by a mechanic friend whom said was worth having because it helps the car better on gas and helps allow the car to breath easier as well. I am a 2nd owner of this car, and the original egine blew on me at 80,000 and the motor I had replaced is a used one from a junk yard actually from another vehicle but, its the same exact type of motor as the original one. The mechanic is thinking someone must have played with the motor before and that is why he wants to take the top cover part of the motor off and see if everything looks good.

Answer
You may have just answered the question for me you said you put a K&N filter in thuis those are notrious for cuaing MAF sensor issue the MAF is the may load input to the engein computer what happens is the oil from those K&N filters migrates from the fliter onto the sensor and that oil collects any dirt praticles that pass by the filetr and screws up the MAF sensor. That is where I would look first and foremost! drive the car with the MAF unplugged and see how it acts It may hesitate but if it acts differently then chance are you found the issue.