I have a problem with my stock '83. When in gear, it decelerates very rough under about 2500 RPMs. It will just start bucking back and forth unless I put the clutch in. I'm stumped, the engine runs pretty smooth other than this...

 

sounds like the coasting valve is not functioning properly.

 

Is that the same thing as the shutter valve? Because I recently replaced it.

 

yes. you may want to check the throttle position sensor (yes it has one!), it controls the timing advance solenoids, and this is active on decel. maybe next on the list would be the anti after burn valves in the ACV

 

Okay thanks for the help. Now, how do I check the TPS?

 

Check all of the motor/tranny mounts, rear end bushings, and u-joints. Drivetrain lash seems to be one of the more common complaints that used RX7s i pick up have.

Isaac

 

I agree with flight! Get under it and check the drivetrain/driveshaft for looseness. I'd guess that to be the weak link.