I have an '86 Iroc with a 305TPI/700r4. This is a project car I restored and got running last fall. The transmission works perfectly fine when in normal drive but in overdrive, when going about 50mph, when I step on the gas the RPMs bounce up and down between 1500 and 1000 and cause the car to rock back and forth. The only way to avoid this is by giving it about half throttle... Any ideas?

 

It sounds like the torque converter clutch is repeatedly locking and unlocking. What do you mean by "when you step on the gas at 50mph"?

Ant check engine lights or engine mods? I suppose it could be an engine surge too. How does it run otherwise?

 

I mean when I try and hold a steady speed anywhere in between 46-55ish mph or even accelerate past those speeds under normal throttle it begins howling/whining and bucking. ONLY in that gear, though. The other gears work just fine.

The only mods I have are eliminated emissions/AC and headers. The car runs fine aside from being difficult to hold an idle at a cold start, and the idle is rather low when warm (500-600 rpms at a stop). The only code the ecu is throwing is 23 which is a throttle position sensor. I replaced the sensor but I cannot seem to do it correctly as far as adjustment goes. I bought a voltometer but it just doesn't work for some reason. The light goes away under hard acceleration and immediately comes back on when braking.

 

getnthe throttle position sensor taken care of first. the ecm doesn't know to lock or unlock the converter because of the messed up throttle position sensor most likely.