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jumping rpms

9

99GP3800GT

New member
i have a 99 gt with 177k miles on it. it runs great for the exception of one thing. when im going about 45 miles per hour and going up a slight hill and accelerate to maintain my speed with the rpms about 1600, the rpms will surge from 1500 to 1700 rapidly. if i let off the gas or accelerate harder it will go away. if i let it do it it wont throw any codes whatsover. it has new plugs(ngk), wires, 3 new coil packs, ignition module, pcv valve, fuel filter, and maf sensor. i also ran seafoam through the intake as well. i dont know if i should go back to ac delco plugs...bad cat...or what??? i took it to a shop when the maf sensor was bad and they didnt find anything wrong. they suggested going back to ac delco plugs but people on here run ngks on here with no problems. my car is all stock with the only mods being short shifter and dogbone flip. thank in advance for any and all help.
 


i had the trans filter and fluid changed as well. the rpms jump from 1500 to 1700 and back to 1500 fairly rapidly. it doesnt feel like a downshift. it only does it on a slight hill and if my rpms are above 2000 when going up the same hill it doesnt do anything. the car runs and drives smooth otherwise. shifts just fine.
 
hmm maybe get it scanned with a good scanner, no auto zone crap. transmission codes are stored in the PCM and will not trigger check engine light.
 
youre pushing it up hill with the converter locked. let off the gas completely and then roll back into it. the converter will then be unlocked and youll be able to give it more gas.
 


hard to say, its under the side pan of transmission... depending on your mechanical skill u might could do it yourself... if not expect to pay 300ish depending on shop labor rates. If thats what it is.
 


almost sounds like a slight trans slipping issue. With that many miles on it, it wouldn't surprise me if the clutches were about shot.

Mine will do that when it's cold. you can hear the engine rev higher all the sudden and then plop right back down to where the rpm's should be.
 
im not pushing it that hard!! its just to maintain speed going up a slight incline. im not hotrodding it or trying to speed up just trying to maintain my speed. my rpms only go up a few hundred to maintain my speed. if thats pushing it hard for GP's then i take back all the good things ive said about these cars. none of my other cars have done anything close to this before. and fyi...i tried doing what you said today and still got the same results!!!
 


hm, everytime mine would surge going uphill id just let off the pedal and roll back into it and itd be fine. my converter wouldnt unlock when i get it more throttle like it was supposed to unless id floor it and get it to shift.
 
i also forgot to mention that when in park or stopped at a red light my idle is a little rough. not very bad but enough to notice...maybe 50 rpm jump and you can feel it a little too. dont jnow if thats normal for these cars but ive never experienced it before in any other cars. and when i accelerate harder it does downshift just fine and be o its way. also when im going like 50mph on the same hill it doesnt do squat. just a smooth drive all the way up it. even when its in the same gear
 
My car has been doing this since I bought it a year ago. I had my mechanic have a look at it, but it wasn't producing any codes. He did say that it was definitely going into lockup too quickly and it doesn't like to come out unless you stab the throttle.

Oddly enough, I had a leak in the intake gasket at that same time and had it replaced. After he replaced it, that seemed to cure the trans problem temporarily. He and I were both stumped by that. The "jumpy" symptoms came back slowly over the course of a month.

I hold it back to 3rd in the city to avoid this problem, but it still does it in 3rd sometimes around 35 mph. I'm thinking the problem may be a bad pressure control solenoid but I can't be sure because it's not throwing any codes.

Fortunately it hasn't gotten any worse, so I haven't been worried about it.
 
trans does not throw any service engine soon light, trans codes are stored in PCM... a cheap ass autozone scanner will not read codes. ALOT of mechanics dont have scanners capable of reading trans codes. scanner HAS to be able to read PCM itself.
 
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