Well along with my Z we also own a 2002 LS Sport sedan with the Ecotec/4T40E.

Just started to notice a slight issue a month ago cruising down the highway at 80 with the cruise control on. The RPM's will jump 100-200 and return quickly. Almost a slipping of sorts.

I've consulted a couple people regarding this and first thing that came out was torque converter, yet I haven't gotten much knowledge/recommendations regarding this issue or exactly what it may be doing and a solution.

I only come here as it has started to do this a little more frequently and even at lower speeds such as 60mph now and my concern has grown as to what's going on. I've gotten no service nor check engine light so I'm left without much to go on beyond the above info. As stated I've only noticed it with cruise control on, but I feel the varying of pedal pressure without cruise keeps this from happening and can't really blame cruise as I just feel it's maintaining speed/RPM allowing the problem to surface but not necessarily causing it.

Thanks in advance.

Is it only happening on the you Z? When was the last time you have changed the fluid?



FU Tuning

? It's happening on our '02 LS Sport.

Only 48,000 miles on it so we've never touched the tranny fluid.

Joe Schulte wrote:? It's happening on our '02 LS Sport.

Only 48,000 miles on it so we've never touched the tranny fluid.

Ok so it is not happening on your Z then. I would change the fluid and see what that does. A really good friend that has a auto Z24 and has put a lot of miles on it (lots at the track) when the fluid gets burnt or old his tranny will start acting funny on him. A tranny cooler would also be a nice mod to help (even on a daily driver). I'm not saying this si the problem, but I have always been told to change auto fluid every 25-30k.



FU Tuning

I will add change the filter while your there, not just a flush. Which is what you'll get at a service center. I waited like you did, and it was packed with gunk. car straightened up right after.

The filter kit is usually only like $20 at the parts store. if you get one and it has the cork gasket, reuse your old one...you'll thank yourself later when it doesn't leak.

If you do a flush, do it now or never do it at all and just change the trans fluid and filter. Your problem does sound torque converter related though. Does this only occur when you are using the cruise control, or when you are throttling the engine yourself as well? Because going 80 mph on a stock engine, chances are, you are close to a throttle position that will put your PCM in PE (power enrichment) mode which would make sense that it appears the engine revs a little, which means you actually don't have anything wrong.


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"Youth in Asia"...I don't see anything wrong with that.

Cinny wrote:I will add change the filter while your there, not just a flush. Which is what you'll get at a service center. I waited like you did, and it was packed with gunk. car straightened up right after.

The filter kit is usually only like $20 at the parts store. if you get one and it has the cork gasket, reuse your old one...you'll thank yourself later when it doesn't leak.

Agree with abnove as well.

Also running 80mph usually puts you about 2800-3000RPMS, at that RPM (unless change with HPT) you require about 60% thottle to enter PE, so I think that statement is off.



FU Tuning

Don't know if the problem was solved yet, but I would check the converting anyways. It's HIGHLY unlikely that it is not but, it doesn't hurt to check, do you know how to do a stall test? Like everyone else stated though, the fluid condition should be checked along with the fluid level. Any how are you certain this issue isn't coming from the engine? Throttle pressure? Vacuum lines? It's just awkward that the engine RPM's fluctuate only between 100-200RPM's...

check the adjustment on the cruise cable

John Higgins wrote:

Joe Schulte wrote:? It's happening on our '02 LS Sport.

Only 48,000 miles on it so we've never touched the tranny fluid.

Ok so it is not happening on your Z then. I would change the fluid and see what that does. A really good friend that has a auto Z24 and has put a lot of miles on it (lots at the track) when the fluid gets burnt or old his tranny will start acting funny on him. A tranny cooler would also be a nice mod to help (even on a daily driver). I'm not saying this si the problem, but I have always been told to change auto fluid every 25-30k.

Nah, all my cars are manuals. Being the other half's car, I had to settle for an auto when we bought it. Thanks for the recommendation though, wasn't sure on recommended intervals for auto tranny fluid.

Cinny wrote:I will add change the filter while your there, not just a flush. Which is what you'll get at a service center. I waited like you did, and it was packed with gunk. car straightened up right after.

The filter kit is usually only like $20 at the parts store. if you get one and it has the cork gasket, reuse your old one...you'll thank yourself later when it doesn't leak.

Good deal, if I recall the flush wasn't horribly priced at the dealership and they even did the filter while in there. Might check into it this week.

Brian Whalen wrote:If you do a flush, do it now or never do it at all and just change the trans fluid and filter. Your problem does sound torque converter related though. Does
this only occur when you are using the cruise control, or when you are throttling the engine yourself as well? Because going 80 mph on a stock engine, chances are, you are close to a throttle position that will put your PCM in PE (power enrichment) mode which would make sense that it appears the engine revs a little, which means you actually don't have anything wrong.

Only noticed it with cruise on as said in original post,.

Caveman wrote:Don't know if the problem was solved yet, but I would check the converting anyways. It's HIGHLY unlikely that it is not but, it doesn't hurt to check, do you know how to do a stall test? Like everyone else stated though, the fluid condition should be checked along with the fluid level. Any how are you certain this issue isn't coming from the engine? Throttle pressure? Vacuum lines? It's just awkward that the engine RPM's fluctuate only between 100-200RPM's...

Stall test? No idea. I'm not 100% it's not the engine, but this definately seems/feels transmission related.

[quote=97cavie24ls(™)]check the adjustment on the cruise cable
I assume you mean the threaded portion on the throttle body?

yes the threaded part

if you can keep the car at 1 speed on a flat level surface with your foot and it doesnt do , and when you hit the cruise and it does it , it sounds more cruise related than anything

Reason I don't pin it on the cruise as it doesn't seem the car moves with the couple hundred RPM increase, it's almost as if the power isn't transferred for a slight moment when the revs go up and it loses speed.

Plus it's so random, it's not like the car is going up hill or downhill etc. where the cruise would regulate the speed.

I'm really leaning towards the engine. If the transmission was at fault for the sudden decrease in engine RPM it would not be between 100-200RPM, more like 500-600RPM. Let's try to eliminate your transmission/converter, first do a stall test:

Connect a tachometer to the ignition system
Set the e-brake
Apply the front brakes
Put the transmission in low gear
Accelerate the engine until speed can no longer increase, note the engine RPM.

Don't do it for longer than 5 seconds and if the RPM's go beyond the stall speed for the 4T40E converter stop the test.

If you decide to do this let me know what happened and I can define the results for you.

It sounds alot like the TCC or torque convertor clutch going out or having some restrictions in the solenoid.
I've been in this issue and believe that when your TCC is disengagine, you'll see that rpm drop you're describing.
Your cruise control will still maintain your speed whether you drop your TCC or not because it's using the VSS and other inputs for your cruise speed and not direct tranny information.

I've had to install a TCC switch for my car because this would allow me to override the TCC whenever necessary to keep the car from doing what yours is presently doing.
I've tried the TCC on/ off with the cruise and the car still maintained good speed with no variations on the settings you set.

Just another idea that no one has mentioned.
Good luck with it.



Misnblu.com
Newbie member since 1999
Thank you Dave and JBO!