I have a 92 RS 305 w/700r4 auto trans. My problem is that when I am driving down the highway with the cruise control at about 60 mph I will be just under 1800rpms and then after a few minunts it will suddenly jump over 1900 rpms for no apparent reason. It will do this on a flat road and I can hear the engine speed up slightly. I would just like to know if anyone knows why this is happening or if this is going to lead to problems. I don't remember it doing that before. Thanks in advance to anyone with some input.

 

Probably your torque converter lockup solenoid is having problems.

 

unstable VSS signal, or unstable TPS signal are my guesses.

 

I have no clue where or what those thigs are. Will I be able to find anything out about them in my Haynes manual??? thanks

 

I dunno because Helms > Haynes

Search for Throttle position sensor or TPS & read a bunch.

It's a sensor that varies voltage and you can check it with a volts meter.

If it returns an unsteady voltage signal to the ECM, the TCC will unlock, giving the rise in RPM you're experiencing.

 

The Haynes manual isn't that good for electrical stuff, particularly EFI sensor related issues. It will cover installation and removal, but not much in the way of troubleshooting.

I agree with jmd about the cause though. I don't believe that this is trans related. Pull the VSS and check the gears for a start. These gears are fairly brittle, and only get worse with time. It isn't uncommon for them to lose a tooth or two, which could cause exactly the kind of problem you're having.

Also check you TPS for tight spots. It should provide a nice linear change in voltage with throttle angle. If there are any jumps or spikes you could have a bad TPS. Also make sure the static setting is around .57 volts. The Haynes manual will tell you how to do this.

 

All right, I will sart searching for all that stuff. Thanks Guys.