2001 Pontiac Grand Prix

Engine Mechanical problem
2001 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 123000 miles

Car was always being taken care of - preventive maintenance and etc.
I was on a hilly highway when I could not climb anymore, I almost felt like driving in nuetral. I drove it in to a local machanic they ran it thru a computerized check and it came back with the following codes: P0131, P0300 & P0404. They diagnozed it and reported that they found a hole in the upper plenum. They replaced the " Upper Intake Manifold", did a complete tune-up (spark plugs & wires, fuel filter & air filter), they also claimed that the fuel pump is bad which is plugging the Catalytic Converter, they replaced both (the Catalytic converter used is not a Delphi part).
It ran fine but I had difficult starting it in the morning or when not used for long period of time (sometimes so bad, that I lost power as soon as I stopped pushing the gas pedal - in park, drive and nuetral), I took it back to them - they claimed that the Fuel Pump is defective and they changed it for me.
Now. The starting issue is better than it was, but I still have a problem starting it in the morning and when not used a period of time - I have to raise the engine (pushing the gas pedal) at the time of starting or it will just not start.
When I left the mechanic the last time they told me that if this will not do it, it might be the fuel injectors. I just put in about $2,200, and I hate to throw good money after bad money. Is there anything else you can suggest?
November 26, 2008.

You had no issues before?
I would check and clean the throttle body
check clean idle air control valve
check for vacuum leaks
are you getting any check engine light (codes )
another local opinion maybe wise too
good luck and let me know

Nov 26, 2008.
The only issue I DID have for a looong time, was (and still is) that with a heavy load and/or on a an uphill highway at approx. 55 MPH I would experience resisting viabration (the RMP guage would jump along with it). But I could get thru it by pushing down on the gas even more.
No codes showing now and no check engine (or any other) light.
So, you suggest that I: 1) check and clean the throttle body 2) check clean idle air control valve 3) check for vacuum leaks
Would you do this with the same mechanic or try another local guy?
Also, should I rather return to the dealership where I serviced it 90% of the time (about the same price range)?

Nov 26, 2008.
I hate to say this but I would try different shop or if you like the dealer do so
good luck

Nov 26, 2008.
I just wanted to thank you for your help last year! After going thru all the suggestions and eliminating part after part, we finally figured it out!

The problem is faulty software on the PCM (Power Control Management) chip that was reflashed and now works flawlessly! I notified GM about it and they act as if this is news to them too (I highly doubt it).

The other issue was resolved (I think) thru a recall repair. The recall said hard braking may cause oil to ignite on the exhaust manifold. Having accidentally caused an oil fire while adding oil to the GTP and spilling a couple drops on the hot exhaust manifold - which answers a whole lot of other questions. I also don't have to add a qt. Of motor oil between oil changes anymore either.

Thanks again, DG

Dec 9, 2009.