“Welcome to my nightmare” Where to begin??? I bought my 97 Grand Prix SE for my Daughter from a “friend” for $500.00. I just wanted it to hold her over until I could repair her other car or buy her a new one. I was told there was a “fuel problem”. When I get the car home I find the Fuel pressure regulator is disconnected. Wow that was easy!!!
NOT!!! No luck the car stalled at HWY speed on my Daughter and left her stranded. It always restarted after a short rest and got her back home. At this time there were no codes. After some testing and reading a lot online I replaced The MAF sensor. Then the MAP Sensor codes started popping up so I replaced that. Codes for map gone but no improvement in drivability. To shorten the story I replaced the O2 sensors the Plenum gaskets, a lot of bad Vacuum fittings, Cleaned the throttle body, replaced the bad PVC valve, the bad valve cover gaskets, power steering pump, Crank and Cam sensor, And bought some new scanner software. None of which fixed my problem. I’m getting a lot of P0171 codes. And on my last test drive I ran for A good 100 miles before it quit on me. I was looking at my scanner on the way to the service road when it started and it looked like my 02’s flat-lined as it chugged along on the HWY. When I checked the codes it gave me a P0131 and the good old P0171. When I got home I removed the throttle body and looked into the plenum and it was soaked with coolant. I think that was what is causing my 02’s to go nuts and also causing my P0300 and P0171 codes and Killing my motor. Remember all the gaskets where replaced. I would recommend if you don’t have a good scan tool that you find a “Good” Mechanic (Good Luck) and get the car on a scanner so you can watch some live data. And if you find this “Mechanic” and he can use a Diagnostic O’Scope he or she can save you a lot of wasted money on part swapping. If you can’t find a Mechanic start with vacuum leaks. Then look for oil and coolent in the plenum. Check the PVC The coils for good resistance and the wires for signs of arcing. Look at the plugs and replace if needed. The MAF also seems to be a big problem. Try disconnecting it and giving it a test drive (this will through a code). Check fuel pressure with and without the vacuum line. And test vacuum with a vacuum gauge. If you don’t have the test equipment. Buy it or have the shop do the checking then do the work yourself and save some$$$$$$$$. Let me know how it goes.
Good Luck
Rich