high RPMs at highway speed

I'm having a problem with my '98 GTP. It's running high RPMs at highway speeds. Normally the car would run about 2100 RPM at 70 MPH. Now it is running about 3000 RPM at the same speed. This started about a week ago. It now also feels real sluggish at those speeds as well. When you step on the gas, it doesn't really want to go - very hesitant.

I've had it at the dealership a couple of times now for them to look at it. They haven't found anything that is wrong. They did do quite a bit of work on it though since it's at almost 100K miles. Most of it was normal maintenance stuff. It had the transmission fluid changed, coolant flush, tune up with new plugs, air filter, fuel filter, PCV valve changed.

I'm not getting any codes off the computer. They even tried updating the software on the computer to see if that would do anything.

Not sure where else to look, or what else to tell the dealership to look for.

Any ideas?

Your tranny may be slipping.

Wondering, how many times is it shifting? Is it going into overdrive?
http://img.photobucket.com/albums/v425/kustomkid54/1998PontiacGrandPrixGTP004.jpg

maybe it is going into overdrive but tcc is not working properly???

tcc lockup is usually only good for 3-400rpms drop, sounds like OD ain't kicking in.

I was guessing the same thing, that it wasn't shifting into OD. I'll have to listen to it again and see how many shifts it makes.

I don't think the tranny is slipping, it seems pretty smooth when it does shift. Is there a good way to tell if it is slipping?

After the software update the dealership did, it seemed to change where the hesitation is. It's now in the 45 MPH range instead of at the higher speeds. I wonder if the computer is having problems with the shift points? I talked to them again, and they want to do a full reload of the software again. Other than that, they still don't think anything is wrong. But it's still at 3000 RPM at 70 MPH.

Mine is doing the same thing. It won't go into OD, and the Torque converter isn't locking up. I am told, the TC slips, and the computer dis-engages OD, and the TC lock up.
When cruising, hit your brake pedal a small amount, and see if your RPM's increase about 300, and go down again, if it does that, your TC is locking up.

i'm gunna go with the OD not kicking in. be careful though. my tranny crapped out on me and it was doing the same thing.

I heard back from the mechanic. He said the transmission solenoid and valve assembly were getting too weak to shift into overdrive. So, it certainly appears to be a transmission problem. I should get the car back today. I'll post back if I this doesn't fix the problem.

post prices too. thanks

Hey Philip.
I went on the internet and did a search in Yahoo for rpm problems, and I found your post. Last night I noticed that my 2000 GP GT 3.8L was making a higher pitch rev noise at high speeds (60 or above) and then I saw that the tach shows rpm at 3000-3200 instead of the normal 2000-2500. Also, I wanted to ask.... Does your temp gauge run a little higher than usual?? Mine shows to be around 190 instead of the usual 175 or so- maybe this is related to the fact that the Overdrive is not kicking in. I first thought that my thermostat was going bad (maybe sticking), but I get plenty of heat inside my car, so maybe it's the transmission problem like you guys are saying this post. Anyway- let me know what you did to fix this- I hope it don't cost an arm and a leg to fix this!!!! Thanks to everyone for their information in the posts.....

OK, the things I've done to try and correct my problem, coming out of OD, and the TC not locking up.
Replaced the Shift solenoids, and the TC lock up switch=$450
Replaced the VSS sensor=$40
Replaced the cam sensor=$120
Retimed the cams(They were off)=did it myself
Replaced the TPS=$40
Replaced the IAC=$40
Had the tranny rebuilt, with a new TC=$950

I just bought this POS, dumped all this money into it, and it is still doing the same thing!!!!!!!!!!

I guess the ECM will be next!!!!!

A good test for overdrive is put the car in 3rd gear. Get up to highway speed (50-60mph), turn on cruise control, and then push the shifter into D. If the car does not change gears (like my car) then the Overdrive is not moving from 3rd to 4th gear.

This site does a good job explaining the Transmission converter clutch.

http://tech.oldsgmail.com/trans_TCC.html

It looks like Overdrive is controlled by the solenoid that gets a signal from the ECM to make the gear shift from 3rd to 4th. There are 2 wires that go to the solenoid- 1 for the 3rd gear and the other for 4th.

Sorry I didn't get back to this. The guy at the dealership replaced the solenoid and valve assemby. He also said he replaced the 4th gear clutch drive shaft. Total cost came to just under $1300. That's with all new parts.

The car runs much better now. I'm not having any issues with the RPMs or any shifting.

2000GPGTBlue2dr, I didn't notice if the temp was running higher. Of course, once this started I didn't really drive the car at highway speed very much. But that sounds like a good guess. If the engine has to work that much harder, it could run hotter.

Phil,
One last thing. What were all the new parts that were replaced??? Was it just the solenoid, valve assembly, and the 4th gear clutch drive shaft?? Did they have to basically re-build the transmission??? How did they get to these parts to replace them, in other words, did they have to remove the transmission, or were the parts accessible from opening up the bottom pan?? I wanna get an idea of everything they did for the $1300....

I took it to a shop and they did a diagnostic test and they found no transmission codes, and I had them change the transmission filter 'cause I never had transmission service before- since I bought the car.

I'm so pissed, man. Even though the car does go into overdrive, I hate driving on the freeway cause the transmission is not going into 4th gear when I press the accelerator at highway speeds- it only goes into overdrive when I release the accelerator. So I hit the gas and it goes to 3000-3400 rpm, and when I release it drops down to 1800 rpm- and my fuel economy went down as well, along with the temp gauge reading higher than usual- this sucks!!!!

Here's a price update on my Grand Prix's transmission.
$1150.00 rebuild/overhaul -they put it inside a cleaning booth to remove all the grease after they took it apart- now it looks as good as new.
$287.41 all new parts -includes the 4th gear clutch hub which was stripped out, 4th gear sun gear that attaches to it, and the torque converter which was the most expensive part ($200)- it was replaced because the fact that the metal shavings from the clutch hub could have damaged it. The rebuild kit also includes all the seals, O-rings transmission filter, etc.
$114.99 tax
1552.40 total

Now my car shifts into 4th gear on the freeway, and all is well.

Make sure you find an honest shop to do your work. Look for the ATRA sign in the window which stands for Automatic Transmission Rebuilders Association. If they belong to this Assoc. the work is warranted at any of these shops throughout the U.S. for 12 months or 12000 miles.

Here is the parts list from the work I had done. Sorry it took so long to post. The total price for the parts (all new) was $585.92. That includes a couple of different gasket kits, the main control valve body ($242) and solenoid ($59), and 4th gear shaft ($113).

Hello;
Interresting that your 98 Grand Prix is/was-doing exactly same issue as my Grand Prix GT. Would not go over 70mph, though read differently. The engine was sounding as if it would rip right-outta the hood, so it was revvvvving but car wasn't responding.

Knew it wasn't the Trani as 60,000 on it,,,usually over+ 100,000 would possibly be Transmission. It infact was the 'Catalytic Converter'. When the mechanice removed it basically it resembled a piece of coal. He then held up what it should look like wich is a finished-metal honey-comb which is fitted into your rear exhaust system.

Fortunately it was covered by Warranty otherwise it in itself is not an expensive part*. Especially compared to cost of the transmission, if infact that is what it is.

Just some input. Mancini ------