Stumble will NOT GO AWAY

[LoveMy02W68]

So about a week ago I went to drive somewhere and noticed that my firebird had an annoying stumble in it. Needless to say the past week has been from hell. I've notice that the stumble I'm getting usually happens when I really get on the throttle. Now onto the list of things I've replaced/checked already...

-New spark plugs. NGK TR55 (they are gapped correctly, I'm positive)
-New plug wires.
-New coil packs
-New K&N air filter
-Checked all my induction work to make sure its sealed alright and it is.
-Checked all my vacuum line replaced a few things that looked worn, still nothing.
-New fuel filter
-New fuel pressure regulator.
-Cleaned MAF sensor

I only run premium gas, although I thought maybe I got a bad batch and tried some octane booster. Still nothing. I'm about to go rip out the EGR and make sure thats working. But for the most part, I'm lost. I'm almost out of ideas and wayyy beyond out of patience. I need my car up and running. Any help would be great.

Also, when the car starts to stumble, it still has pick-up and still accelerates. It's just really rough and the RPMs slow down. It's not constant, like I said only when you really give it gas. Also tends to come and go in how bad it is.

[Bobd1001]

Re: Stumble will NOT GO AWAY

Bad Catalytic converter?

[ACiFiC]

Re: Stumble will NOT GO AWAY

Throwing any codes?

[firebird19_99]

Re: Stumble will NOT GO AWAY

maybe etc?

[ssms5411]

Re: Stumble will NOT GO AWAY

X2 on bad CAT.

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

CAT is still good. It's a new magnaflow only about 2 years old.
Also, not throwing any codes.

[ssms5411]

Re: Stumble will NOT GO AWAY

Maybe a clogged injector or one injector is starting to go. I had one injector that was bad and it took me a year to find out.

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

That's my next step. It's just getting costly and time consuming to keep guessing and buying parts. I'm trying to find a GM tech around here (central NY) to look at it so if it is in fact an injector he can tell me which one. But thanks for the suggestion I'll definately check those next.

[pace2006]

Re: Stumble will NOT GO AWAY

Before you start tearing the engine apart or pulling your PCM, you might try testing your TPS or crank position sensor to see if they've gone bad. ICM could be another culprit, but that's an expensive part and can wait til other more common issues have been checked.

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

I'll give those a shot too, thanks. I was going to pull the injectors but I was thinking that the stumble only happens when I give it alot of throttle, so if it was an injector it would be more constant even during idle, right?

[kristen]

Re: Stumble will NOT GO AWAY

i wouldn't blow of the cat that fast. mine went out and never threw a code. and just because it's 2 years old, doesn't mean anything.

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

Alright I'll double check it. It's strange though because between the time it was running fine and when it started to stumble was literally over night.

[WarShrike]

Re: Stumble will NOT GO AWAY

Cat
Crank/Cam position sensors
PCM
Bad compression (do a compression test). Could be a bad head gasket or even a worn out valve or seat.

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

Replaced fuel filter and fuel pressure regulator and im getting only 40psi of fuel pressure. Fuel pump maybe?

[LoveMy02W68]

Re: Stumble will NOT GO AWAY

I just took it around the block a few times and i noticed that once the stumbling starts (3500-4000 RPMs) the RMPs stop rising and just sort of sit at where they were when the stumble began.

So if it starts at 3500 the needle will just sit at around 3500 until it shifts into the next gear, then the drop back down.