transmission problem

i'm pretty sure this question has been answered a billion times, but i just want someone to tell me, to make me feel better about the situation. my transmission feels like it studders, or slips maybe when i get on it kind of hard. but only in first gear. sometimes it shifts hard too, not neccesarily when it's cold or hot...just kinda random. i've read some on these forums about "P1811" being a code that the transmission gives out. it seems like the symptons of this code kinda match what mine does. my car has 138,xxx on it. the guy who i bought it from said when he bought it, which was only a year ago...when he changed the oil and had the dealer swap fluid and filter, that's when it started doing it. if this is the case, what is the best route to fix this problem, and approximately how much will it cost, assuming i do all of the work?

What year and model Grand Prix? If your GP has a 4T65E autotransaxle see the link below which will take you to our Tips & Maintenance section.

Click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=920671)

it's a 97 gtp

Then you have the 4T65E-HD GM RPO Code MN7 transaxle. The procedure and guidelines in the Tips is applicable. Start by getting it scanned with a trans capable scanner and see if a P1811 DTC is stored or get the line pressure checked.

Also, are the symptoms the same with performance shift ON?

i actually don't know for sure, but i think so.

If it is acting up with Performance Shift on or off them most likely a line pressure issue which would explain the hard shifts. See if the P1811 DTC is stored indicating the shift timing is off. When off the P1811 should set. It does not give a SES/CEL light but will store for retrieval with a scan tool/scanner.

the only thing is it doesn't do it all the time. it's only once in awhile, but it studders all the time...

Studder or shudder or is it more like a misfire condition? Shudder can be caused by abnormal line pressure and/or the P1811 issue.

it's definately not misfire. it only does it in first gear...it feels like wheel hop...in the engine bay.

update: i went out for a drive, and put it down in "1" because someone said it has increased line pressure...and sure enough, it didn't studder at all. i actually broke my tires loose a little bit, which was nice because i've never done it in this car. so....i'm guessing this means i don't have enough line pressure in drive. what's the solution for this problem?

I'm not sure that in manual low you have increased lin pressure. In fact with performance shift turned on, you also have increased line pressure.

In manual PCS line pressure control operation is inhibited and line pressure goes to other values. Based on the symptom this is more like launch shudder. Same issue I had with my GTP over 4 years ago. I replaced the PCS solenoid and added a shift kit. And there was a P1811 (max adapt, long shift) DTC. Shift timing was greater than .65 seconds which causes the DTC to set and then commands maximum line pressure and disables shift adapts.

so i'm 95% sure the pcs is my problem. i know someone who will charge me $100 labor to take it apart and replace it. my question is, being as i have to pay for parts, how much is it for a new pcs? what about the tcc solenoid? gaskets/other parts?

That is very inexpensive for labor considering the type work involved. Most tranny shops will charge around $500 and up just for labor. The PCS solenoid costs around $50. Get the Borg Warner brand. Since the transaxle side cover is removed you should get new side cover gaskets. Up to you if you want to replace the TCC-PWM solenoid or any of the two shift solenoids.

the guy who will do it for me said i should probably replace the tcc solenoid. how much is one of those, and the two shift solenoids? are they worth replacing? where can i get these parts?

All the solenoids run around $50.00. You can get the parts at the GM dealership, Autozone, Advance, or internet parts sites like rockauto.com or gmpartsdirect.com.