Beretta.net

Bought my '96 Z26 cheap 3 years ago, knowing that the transmission (4T60-E) was toast. The local tranny shop rebuilt it 3 times before giving up, and installed a GM factory rebuilt unit. It has worked flawlessly until about a month ago...

When driving at normal highway speeds, give it a slight gentle push on the accelerator, and the RPM's go up about 500 - hold the throttle there for a couple seconds, and it drops back down to the previous RPM. Outside of this, it shifts perfectly - no slippage on acceleration, smooth almost undetectable shifts, etc... 25,000 on the new transmission, and the tranny fluid look perfect - red, with no darkness in it all. I don't beat the car, and the fluid has no burnt smell to it - unlike the previous unit. I check the fluid level regularily, and never lost a drop.

Here is where it gets weird... I don't notice this happening when using the cruise control! It is almost like the torque converter lockup isn't working correctly, but only while manually accelerating.

This has me stumped, and am curious if anyone else has experienced this, or has any ideas of what may be causing this - have never seen this with any of my previous Beretta's. Thanks in advance!!!

Lars

Try moving your foot slower and see if this problem goes away?  You did say gentle push so perhaps there are jumpy spots in your TPS?  It is common for the TPS to get a worn spot in it where the highway speeds are.

It's funny that your cruise would not do the same though.  With a computer controlled tranny it is hard to tell without knowing what the PCM parameters are.  The 4L60E in my wagon has different shift points and TCC lock and unlock MPH when in cruise mode, so anything is possible.

I have noticed mine doing the same thing before.  I always figured it was the transmission coming out of overdrive and back down into 3rd for the acceleration.  Does the same exact thing though.  If I hold it there, the RPMs do fall back down.  The transmission still shifts nice and strong and as far as I can remember, it's always done it.  It has 178K miles on it with only a couple  slippage instances 2 years ago, cured with some seal conditioner in the tranny fluid.

I finally found time to replace the TPS Wednesday night - same issue. As the tranny is relatively new, I am wondering if maybe this is a computer issue? I have been told that there are a few computer firmware updates to fix issues on this POS transmission, but don't have access to that info - $$$. Any leads would be greatly appreciated!!

Lars