My First GTP experience - Won't rev past 2k - HELP!

[thetastywarrior]

Hey everyone, long time lurker, first time poster here. I buy and sell cars, have been for years and worked on my fair share of new and old GM products. Earlier Today i purchased a 2003 Grand Prix GTP from a recently widowed friend of mine. Knew nothing about the car been sitting for about a year. $300.
Formalities out of the way, I got it started up and it idles on it own will not rev past 1.8k-2k and causes horrible shaking.
In gear the car can barely pull itself in to the driveway. I've checked all the normal stuff, plugs, wires, injectors, MAF, vacuum leaks, etc. Everything checks out. I even disabled the injectors (with HPT) one-by-one to see if there's a problematic cylinder, no problems there.
The only DTC I've experienced is P0300 (random misfire of course). And the only abnormality I've noticed is highly fluctuating STFT, somwhere between -5 to -25 rapidly. O2 sensor seems to be responding appropriately.
Is there something I'm missing???

I'm about to head to the store and pick up some fuel system cleaner, maybe that'll help.
Thanks, Levi.

 

[Fivefingerdeathpunch]

Not sure how the misfire didn't just kinda scream at the problem. If the misfire and shaking is so bad, that should be looked into.

Check the plugs and wires. See how strong the spark is at the coils.

Possible that even the exhaust is completely clogged at the cat converter and not allowing it to rev. You can remove the upstream o2 sensor to give the exhaust another escape route, see if the car can rev higher or just loosen the downpipe at the rear manifold to allow the exhaust to escape before the cat converter, then see if it will rev higher.

 

[thetastywarrior]

Check the plugs and wires. See how strong the spark is at the coils.

checked all the normal stuff.. plugs, wires, injectors, MAF, vacuum leaks, etc. Everything checks out.

the exhaust is completely clogged at the cat converter and not allowing it to rev...

And this was the problem, Cat was clogged. Just cut the exhaust gutted it and welded it back together. Good as new.

 

[Fivefingerdeathpunch]

You will get a check engine light now for a cat code, so just be aware of that. If you see reduced fuel mileage that will also be why. The computer will run a cat test because it's not seeing the correct readings by the rear o2 sensor.

Sometimes spacing the sensor out of the exhaust stream fixes it but sometimes not.

 

[bandook]

He's got hpt. He can just disable the tests.

 

[Scottydoggs]

He's got hpt. He can just disable the tests.

no he cant, need dhp and tiny tuner for that. he can delete the codes, but thats as far as it goes. only way to kill the testing is with dhp. dont kill the test it runs rich. unless you can fake it out via the o2 simulation by pulling out out the pipe with them bung extenders things.