i noticed the other night when i was going like 45mph, the rpms were bouncing slightly between 900 / 1200 rpm. idles normal parked / in neutral. what would cause this?

Sounds like the transmission can't make up it's mind, but it shouldn't have shifted yet if it's that low in RPM. It sounds like it shifted to 4th too early and can't decide whether to lock the TC or not. Usually it won't stay in 4th unless it would be turning at least 1500 rpm. Is the car bone stock or has it been modded/tuned at all?

_________________


98 GTP (RIP 11-5-09); 73 Z28 Camaro (350, TKO 600);01 Monte Carlo SS (L36, L67/L32 hybrid in the future)
"Death smiles at us all; all a man can do is smile back"

Sounds like torque converter lock/unlock to me as well. Out of curiosity, try driving at that speed, but press the brake pedal just enough to illuminate the brake lights while keeping your foot on the gas pedal, doing so will unlock the Torque converter and should keep RPM's at the 1200ish you've described.

_________________

Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

as far as i know its stock. i just bought the car its not even on the road yet. and ive had another gp wit tcc issues. its wasnt like that. someone on another forum said it could be the altenator. im just looking for a second opinion. this also is while of the throttle coasting

-- Mon Dec 26, 2011 4:37 pm --

as far as i know its stock. i just bought the car its not even on the road yet. and ive had another gp wit tcc issues. its wasnt like that. someone on another forum said it could be the altenator. im just looking for a second opinion

Alternator is not going to cause that type of issue. I've had bad alternators in the past and that did not happen.

_________________


98 GTP (RIP 11-5-09); 73 Z28 Camaro (350, TKO 600);01 Monte Carlo SS (L36, L67/L32 hybrid in the future)
"Death smiles at us all; all a man can do is smile back"

it doesnt do it wot, just while coasting off the gas. my gt had the tcc issue. rpms would bog down wot tap the brake and it was good. but this is just off the gas rolling. its almost as if i was lightly taping the throttle.

What year is the car?

_________________

Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

99 . 175k. new plugs and wires

That is about the speed for overdrive (4th) and TC lockup, so that solenoid could be failing/bad.

_________________
One Big Ass Mistake America

TC usually won't lock up until around 50. At least not in the w-bodies I've had. Anything slower than that and it locked up at like 1300RPM. but it does sound like a bad solenoid to me.

_________________


98 GTP (RIP 11-5-09); 73 Z28 Camaro (350, TKO 600);01 Monte Carlo SS (L36, L67/L32 hybrid in the future)
"Death smiles at us all; all a man can do is smile back"

The TC lockups on the 97 between 42-48 MPH depending on load (granted that is a 4T60 though). Never really paid that much attention to other 4T65's I've driven though but I do recall it being around 45 MPH.

-- Thu Dec 29, 2011 1:16 am --

If the problem isn't happening while idling and only happening while coasting while still in gear, then it's some sort of trans issue, other than TC/solenoid issues though I've got no other ideas, but I know what it's not..... an alternator

_________________

Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

its common for 3800's to have a 40mph bog, most everyone that's had 3800 have this, even some with heavy mods. a tune might get rid of it, but it almost may not. just a common downfall.

i had the same issue with my car granted its a 2000 with 4t65 e for about 4 or 5 months n went through the lock up solenoid. didnt cure it i did the intake gasket n the problem was gone for sure if your motor is not running right the trans won't make up it's mind

Skip shift and zero delay PE fixes that quite nicely

_________________

Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

My cars been doing the same thing as his, except mine rarely does it. However, I do get the 40mph bog pretty often, unless I'm in perf shift lol

_________________
http://www.cardomain.com/ride/3934864/1999-pontiac-grand-prix-gtp-coupe-2d My GTP
Mods:Ubend Del, FW Intake, GTX Tips, HID Headlights, Euro Tail Lights, Shift Kit, Cat Del, XplOd Head unit, amp, and 12" sub
00 GT99 Silverado05 Malibu
99 Avenger00 Express Van