Idle speed fluctuation problem
 

Hi all ,
My Rx7 FD3S car can't maintain a constant RPM after releasing the choke at idle; it fluctuates between 900 and 2000 RPM. Even after resetting the Apex FC, the problem persists. What could be the reason?

Most likely a vacuum leak, dirty/failing BAC valve, or misadjusted TPS. These cause the ECU to constantly chase idle, leading to RPM hunting. Since a Power FC reset didn’t fix it, it’s likely a mechanical issue, not tuning.

There are at least a few calibration problems which could cause hunting idle, too. Some cells in the fuel map being too lean or too rich, or the MAP sensor not reading properly, or the injector settings wrong, or the IAC settings wrong. I agree it could be mechanical like a vacuum leak or the idle air bypass screw in the throttle body adjusted wrong. Electrical problems could do it too, like poor connections or loose / partially broken wires.

Also, nothing on the speedometer works. More precisely, the gauges work when I turn the ignition on, but they all stop working when I start the car.Could this malfunction be due to a negative terminal problem?

I did everything they told me to do, but nothing changed.😕