My car has been running fine except for one problem, when i drive it and shut it off and start it again it shakes and stumbles.If i wait about a half hour it will start up fine. I have replaced numerous parts including the fuel injectors and fuel filter.I think its the fuel pressure regulator. I had a mechanic replace it a few years ago. Do they usually go bad like that..I'm thinking its the regulator causing my problem,Anyone else have a problem like this, Thanks for any help, much appreciated.

 

Could be a number of things.... might be as simple as a dirty IAC (idle air control) valve (the larger one that pokes out of the top pass side of the throttle body; TPS (throttle position sensor) is the flat one under it). You could try pulling that off (careful with the screws) and spray any carbon off with carb cleaner or somethin similar. If you want to check your fuel pressure reg, pull the vac line off of it on the fuel rail and see if any fuel comes out (might be tricky, but you should be able to get your hand in there without unbolting anything). If any fuel comes out of that vac line, the FPR is most likely bad again.

TPS is another common part to go out on these motors, pretty much every 2.8/3.1 owner I've talked to in the last decade has had to replace theirs. As I said earlier, it'll be the sorta flat one on the pass side of your throttle body, beneath the IAC. Usually throws a code when it goes bad, but not always. When my TPS went bad about 7 years ago, it would run decent-ish, but it'd die as soon as I put it into reverse. This was a consistent issue though, not seemingly heat-dependent like yours.... next time you have the stumbling issue, might be worthwhile to unplug sensors one at a time to see if anything seems to change, don't wanna just suggest that you gotta start replacing everything. I'd check the IAC, TPS, and IAT (intake air temp sensor, it'll be near your air filter).

You could also try just giving the car a little bit of throttle on a hot start... nothing crazy, but if it stumbles and starts to die on you, maybe try hitting the throttle to get it up to 1500-2000 rpm or so and see if it evens itself out. I've had this happen to me randomly on a few occasions over the last few years, still not sure why, but it usually figures itself out after a couple seconds of throttle

 

thanks for the help.I will check it out what you mentioned.