When you start an rx-7 on a cold motor, the idle shoots way up. If you put the car in gear, the idle comes back down.

My car doesn't do this.

However, my problem is similar. My car will idle around 900 rpm. If I tap the gas, the idle goes up to 1500 rpm. If I put the car in gear, the rpm will drop back to 900. If I take it out of gear, it will stay at 900 rpm until I tap the gas again. WTF?!

 

FSM, thermowax cam.

 

thanks, I'll check that out

 

You should also check that the throttle cable is not binding.

The neutral switch on your transmission is responsible for idle changes in or out of gear, so you may also want to check that it is plugged in.

 

Just for fun, next time it idles at 900 rpm, slowly rev the engine til it climbs just up to 1100-1200rpm. I believe you will see that once it reaches approx 1100rpm, it will suddenly jump up to approx 1300-1500 rpms. Then let off the pedal and see if it remains at that high figure. Or not. You don't have to dump the clutch or put it in gear when you do this.

Somewhere around 1100-1200, the ECU advances the timing and that is what causes the rpm to suddently jump up to approx 1500 rpm. Now just why it does not return to the 900rpm once you let off the throttle ..........I know not why not.

Personally, I'd lower the idle speed a bit down at least a hundred rpms. The water thermowax might very well be why it's hung up around 900rpm.