Car sputters when accelerating hard

**joemama22** · 09-07-2010

I am new to this forum and was hoping for some assistance or someone with the same issue. I have a 2005 GTP Comp G. I bought the car with 30,000 miles on it. Once in a great while, it would sputter when I would acclerate hard. I took it back to the dealer and they could not find anything wrong. That was about two years ago. It now does this everyday. Everytime I hit the gas hard, it gets up to about 3500rpm and sputters without shifting into the next gear. If I let off the gas, it shifts fine. I have seen several links with somewhat similar problems and it seems there could be several fixes for this like MAF sensor, CAT, and Shift Solinoid.
Any help would be much appreciated. This is my second GP and I absolutly love it.

**gtpsleeper** · 09-07-2010

does it feel like its sputtering on a shift? cuz mine did this once... changed my plugs and it was taken care of... so if it doesn feel like its on a shift id check that out

**CTKGP09** · 09-07-2010

how many miles on the car? i was gonna suggest plugs too

**joemama22** · 09-07-2010

It sputters at the point when it should shift. But it wont shift unless I back off on the gas. This problem gradually got worse in the last couple of months. I bought new plugs and wires tonight and will try that tomorrow. I also ordered a new CAT. Should be in tomorrow. I tried looking at the MAF sensor but one of the torx heads stripped so I cant get it off to clean it.

**joemama22** · 09-07-2010

Oh yeah, It has 70,000 miles on it.

**rynoman03** · 09-08-2010

Originally Posted by joemama22

It sputters at the point when it should shift. But it wont shift unless I back off on the gas. This problem gradually got worse in the last couple of months. I bought new plugs and wires tonight and will try that tomorrow. I also ordered a new CAT. Should be in tomorrow. I tried looking at the MAF sensor but one of the torx heads stripped so I cant get it off to clean it.

Use needle nose vice grips or take a dremel to it and make it a Slotted "Standard" screwdriver head by taking a cutting wheel to the center of the head just enough to make a screwdriver fit in there.

**gtpsleeper** · 09-08-2010

post what happened after the plugs... my advice would be to not just start throwing parts at it untill you figure out whats really the problem.... youll waste alot of money that way IMO :/

**EJOUIE** · 09-08-2010

not sure if we have exactly the same problem, but mine is doing something similar. First gear is fine. WOT all the way, no prob. 2nd gear is rough. really noticeable at 3000 rpm and above. car struggles to reach third. Doesn't seem to sputter but more like it stops accelerating for a quarter second then continues for the rest of the second and repeats. The engine doesn't sound like its cutting out at all. more like the transmission is going into neutral, but it isn't. and it causes the SES light to flash. going to see what code it set off tomorrow. anyone wanna guess? its a 97 gt with the 4t60.

**TheOtherNick** · 09-08-2010

Pull the front 02 sensor out and drive it, if it is better your cat is clogged.

**joemama22** · 09-15-2010

Thanks for the replies everyone. I went and bought spark plugs. I couldn't get them in my self, because you pretty much have to move the engine forward a few inches to get at the back ones. I took it to a local mechanic and he suggested I get the CAT replaced first. He use to work at the dealership down the road and said he thinks my CAT is still under warranty. He called the dealer for me and sure enough, the cat is warrantied for 8 years/8,000 miles. Even though I bought this car used without a warranty, they still warranty the CAT because of emmisions. The mechanic at the dealership checked out the car and thought it might be the CAT to. He wasnt a 100% sure, but they will be replacing it tomorrow.

If this fixes it, I will let everyone know. Otherwise I will be trying the MAF sensor. Thanks again everyone.

**Tengis** · 09-16-2010

few inches to get at the back ones.

I have long arms + massive forearms and I can get to all plugs easily in modified or stock engine bays without moving anything.

Whenever I have had this issue with a car I will spend 25-30 minutes and check the spark plugs for cracks, check the wires and/or swap out a set with a known good set to see if thats the problem before buying a set for that car, swap out the ignition coils with known good ones from another car, swap out the ignition control module with known good one from another car.

**joemama22** · 09-16-2010

Well it turns out it was the CAT. After changing it, it runs better than when I bought the car. The whole inside of the CAT was broken in pieces.

Now I just have to figure out whats causing the Service ABS, Service Brakes, Service Stability Control, Service Traction Control, and Service Variable Effortless Stearing lights to go on. The car runs perfect, so Im not sure why these lights are all coming on. Let me know if anyone else has this problem.

**mlasnoski** · 09-16-2010

What is a good website to get a Catalytic Converter. I did the GM Parts website and it was almost $500 for a new CAT. Thats pricey! Is there a cheaper and perhaps just as good quality some where else. I have a 2004 GTP CompG with 100,300 miles. I perhaps may have the same problem and with that many miles anything is possible. Everything else seems perfect. I had the tranny filter and fluid flushed and everything checked out fine. I also had them replace the spark plugs and fuel filter. It just seems like it doesn't want go like go from a stand still. Maybe its just my imagination I mean I was use to driving a Grand Am. There is more car on a Grand Prix so I assume its going to be a little slower of the line. I also should with 100k just replace the O2 sensors now? Perhaps it would just be beneficial. UGH cars are money pits even though I LOVE HER.

**blueguy** · 09-17-2010

If you have never done it take off the throttle body and clean it. The '04+ Drive By Wire cars are known for having issues with gunked up throttle bodies and it causes all sorts of issues...such as rough idle, hard starting, sticky accelerator, etc. That's free too. As for the cat if your dead set on that being the issue...you can get a universal magnaflow converter off of ZZPerformance or off of EBay for under a hundred bucks shipped to your front door.

**joemama22** · 09-18-2010

It probably is your CAT. My CAT was going bad since the day I bought my car. The dealership I brought it to when it first happened could not find anything wrong. Over the next two years it got progressively worse.
With the new CAT, this car has unbelievable torque. I cant believe how quick this thing is off the line. It wasn't this fast when I first bought it. I cant wait to start doing some modifications and make it a little faster.

Also, I initially bought the CAT at Autozone for $91. They had to order it and it came in two days. Luckily my car was still under warranty and I was able to return it for a full refund. But I still cant believe what a difference it made. Now I just have to figure out whats wrong with all the service lights popping up. I think it may be one of the wheel hubs. Not sure though.