Trans Problem

[jason1351]

Ok, this has happened a couple times now. Going down the freeway at around 80mph and I notice the RPM's are around 3500. Usually it's around 2200-2300 at this speed. Once I stop and turn the car completely off and restart it and get on the X-way, RPM's are where there supposed to be and no more problems. My car has done this twice now, first time being about a month ago, and this morning. Anyone have any ideas as to why? Trans only has about 30,000 on it straight outta GM and shifts normally except these 2 times when it's not shifting outta 3rd.

[gtracing96]

idle positioning sensor... my moms GA had the same problem... does it idle higher as well?

[rixGAphx]

idle positioning sensorGA has no such device.

The idle is controlled by the Idle Air Control (IAC) valve/motor.

The engine running speed (above idle) is more complex:
* The throttle cable (from the pedal) opens and closes the throttle plate (inside the TB, Throttle Barrel (or bore)); that precisely-controls how much air goes into the engine.
* On the side of the TB is the Throttle Position Sensor (TPS), which measures how 'open' the throttle plate is and tells the 'puter (PCM).
* From this, the PCM determnies how much power the driver wants, and determines the fuel injection accordingly (and adjusts it with a lot of other data).

So, if the PCM doesn't "see" the throttle as wide-open (because of a faulty TPS), then it doesn't know the driver wants more power/rpm.
BUT, the tranny should ALWAYS upshift to 4th above ~25 mph, unless something is keeping it low: Acceleration load, or something else.

My *guess* is that your shift cable is slightly out of adjustment, and you were actually in 3rd gear even though it indicated 'D'.
So it was the shifter setting holding you back, not some tranny or engine problem.
How does the PCM know what gear your in? At the tranny, next to the shifter cable attachment, is an electrical plug with several wires. Just inside is a switch, the Transaxle Range Sensor, that reads what the cable does and sends the data to the PCM.
Check at this location on the tranny (near the firewall, kinda below the mastercylinder) for looseness of the cable, conncetor, etc.

Next time this happens, try shifting into 'N' (won't hurt anything, my dog does it all the time :roll: ) then back into 'D'.
Frankly, you should be in 3rd all the time, except when you get on the highway then upshift to 'D' for fuel economy at 50+mph.

Hope this helps,
-Rick

PS:
Everything I wrote, from 'guess' onward, *assumes* that the car did not upshift into 4th while driving to the highway.

[jason1351]

Already did the "N" shift check(my girlfriend does it all the time) and nothing affected the shifting. The only way for it to start shifting into 4th is to pull over and shut the car off, then restart. I'm taking it into a friends shop to get checked out next week sometime. Hopefully he can find the problem. Thnx for the replies.

[Jasonldrummer]

I am having sort of the same problem.
When I travel down the highway at speeds around 65 or 70 my RPM's are around 3000 and 3500. I drive alot of highway and this hasn't been the normal RPM's. Also, when I let off of the gas "at those speeds" the tach drops quickly to 1000 rpm's not like my other car which drops slowly as the car slows down. Almost seems like it's not shifting into 4th. gear.
If anyone has any solutions or advice that would be great!
Thanks

[GrandAm2000se]

Clutch plates have almost or no friction left on them, therefore causing them to slip, or it might be time for a trans fluid change.

Where I would go since you only have 30,000 miles on the tranny, change the fluid and filter and put some AMSOIL Synthetic ATF, that will be your best bet. (jason1351)

As for you Jasonldrummer, how many miles are on the vehicle, and when was the last time you changed your transmission fluid?

[Jasonldrummer]

221,000 miles on the vehicle and it's been quite a while since there has been any tranny work done or fluid changes. I know, I know it should have been done a long time ago but, I thought it was one og those things where after so many miles you should change the fluid. I was thinking about doing it myself... any advice?

[GrandAm2000se]

Personally, I would leave it alone. If you change/flush, (same meaning) the tranny fluid you might make it worse, because the grit and dirt inside is whats making the tranny not slip as bad. DO NOT POWER FLUSH IT, which removes almost all tranny fluid.

DO WHAT YOU WANT, if you have that many miles on the tranny your pretty much out of luck anyway, if you have the money to replace the tranny, go for a fluid change, or just leave it, don't make a difference.