Hi all I hope you all can help me out. I have a 2000 Pontiac Grand Prix GT which had the dreaded P0171 code and the culprit was the MAF. Before I changed it it would stall sometimes while waiting at a stop light and it would seem to want to stall while driving and it would catch itself. We replaced the MAF and now a new problem has occured. When I took it out for a drive it hesitated and would not go above 25 mph and when I stopped to do a u-turn it stopped hesitating and was fine after that. I returned to the shop and I went out with the tech and had to do a long test drive for it to do it again. The car has plenty of power under acceleration. We went back to the shop and he hooked up a fuel pressure gauge and went back out on a test drive and it was in specs and no hesitation. Any ideas what it could be? It only hesitated twice and now seems to run ok.
I replaced the fuel pump in October 2010 and recently replaced the fuel filter and PCV. When the engine was rebuilt in Feruary 2011 all vacuum lines were replaced.