Thread: '99 GT Chugging problem

I just bought a '99 Grand Prix GT with 162,000 miles on it, and have been having some problems with it. At highway speed (anywhere from 45-60) the RPM's seem to fluctuate about 200 RPM in fourth gear. It almost sounds like it shifts, but it doesn't. At 55 it fluctuates from about 1700 to 2000 back and forth. It seems to chug and "buck" as some people have described it going up hills also. I have seen that many other people have had this problem, but I never really found a good solution. There are currently no check engine lights on. I took the MAF sensor out and it looks like one of the four wires is discolored/corroded, but I put it back in and unplugged it and drove it with no change. I have also read that some people say it could be a bad throttle position sensor. That will be next on my list. I just wanted to see what you guys thought.

Could be any number of things.
How are the plugs and wires?
Could be a crank sensor starting to go(had em at the shop where they didn't throw a code)
MAF
Fuel filter original?
Fuel pressure good?
Could be a connection in the ICM, or a coil pack starting to crap out.

Question is, how many parts do you want to throw at it before you either sell it, or take it to someone with the tools and knowledge to fix it? You could always do the fuel filter and tune up yourself and if that doesn't fix it consider taking it to a shop. They are both fairly cheap/easy, and are probably needed as far as matinence anyway. Maybe get some MAF cleaner and try that too...

I really don't want to throw too many parts at it if I don't have to. I'm not taking it to a shop, because I have the tools and the ability to fix it. I'm just looking for advice.
I'm going to start with cleaning the MAF and possibly testing the TPS. The plugs are brand new and the wires look fine.
I would assume the fuel filter is original.

Will do. I used Bosch Platinum Plus.

Fair enough, I would do the fuel filter too if it will come off easily.

I won't get to it until Saturday. I'll let you know how everything goes. Thanks for the help.

Cleaned IAC valve. TPS tested good. Changed transmission filter & fluid. Seemed like quite a bit of metal in the pan to me, but it's the first pan I've ever dropped. I took it for a drive and the RPM's didn't vary at all on the flat highway. I put it on cruise and found some hills and it still did fine. I hit the gas going up a hill and it still shuddered. I went on a 63 mile drive back to school today and it was acting just like it started. RPM's varying, clunking into gear once it's warmed up. What do you think?

Also, I replaced the bulbs behind the DIC. (Wagner PC119's is what I used) It got very hot today. Almost to the point where I couldn't touch it.

Mine was the ecm

How did you end up finding that out? What about this torque converter solenoid I've been reading about?

Originally Posted by dustin033

How did you end up finding that out? What about this torque converter solenoid I've been reading about?

Simple after 6 moths of futzing with in and it dying on the road a miles from home I had it towed to a shop sat there for 3 days without giving him the problem finally he decided to just keep driving it after about a half tank of gas he got stuck had so he to figure it out so he could get it home lol

Anybody else have any input? Any tests or recommendations?

I took it to a transmission shop today. Of course it didn't do it when he took it out and drove it. He hooked his scanner up and it pulled a P1811 and MAF & TPS low voltage. He said they would replace the TCC and EPC solenoids, two shift solenoids, and install a shift kit for $650 + tax.