02 3.8 nightmare

[cmauto]

i own an auto shop and a was brought a 2002 grand prix 3.8 no super.
the car will idle fine but when rpms are brought up around 2 grand acts like
it has a rev limit rpm goes up and down if let off gas car will die but will restart.checked fuel pressure was 8 pounds below specs. put new fuel pump and filter didnt fix it.prior to this i did check iac and tps with otc scan tool
also cleaned iac motor .after fuel pump i tried fuel pressure regulater didnt fix it.i then tried new plugs still didnt fix it.oil smell a little like gas so i thought
it was worth the shot changed oil nope still didnt fix it. noticed intake is leaking anti.sprayed carb spray around does not seem to have vac leak.there are no codes stored in history or anywhere else.this is my first time on this site and would be greatly in debt if anyone has had this problem before and can help i dont know if i post my email or not but here it is
[email protected]

[cmauto]

i own an auto shop and was brought a 2002 pontiac grandprix with a running problem.car will idle but when brought up to 2000 rpm seems like car has a rev limit rpms will start going up and down,if let off the gas car will die but restart.checked iac motor and tps with otc scan tool seems to working ,cleaned iac anyways didnt help.checked fuel pressure was at 48psi specs showed it to be at 58psi. changed fuel pump and filter did fix problem.then replaced fuel regulator still didnt fix it.changed plugs didnt fix it.oil smelled a little like gas changed oil didnt fix it.intake leaking little anti but checked with carb spray for vac leak didnt find one. car has no codes stored or in history. if anyone has had this problem or can give me hint i would be very gratefull this is my first time to this sight and am not sure how to do this so here is my email [email protected]

[BNaylor]

Welcome to AF.

What are the current fuel pressure readings? At fuel pump prime, ignition ON and when engine is running at idle.

Another issue on 2001-2002 Grand Prixs with the SII 3800 engine is a defective/clogged CAT convertor. GM extended the CAT warranty to 10 years or 120K miles as a result. Engine will either die or act erratically at a range of 2000-4000 rpms due to the excessive exhaust backpressure. Run a vacuum test at 2000 rpms and idle with a typical automotive vacuum gauge (0-30 in hg) and see if vacuum is in specs (15-22 in hg).

BTW - 58 psi is not typical. 48-55 psi is. And it depends on whether vacuum line is connected at the fuel pressure regulator or off.