I have a 1989 GXL. I am experiencing an idle issue. When the A/C is running there is enough draw on the engine that it is not an issue. Without the A/C running it has a good base idle but then surges down and will sometimes stall. It will always start right back up.

Any suggestions on what it might be?

Thanks!

 

Here is the deal. The rotary engine has so little torque at idle that half of the stuff on top of the motor is for idle speed control. The BAC is the main controller of idle speed but it needs help with suddenly switching loads like AC or heater fan on high. These accessories have signals to the ECU to open a vacuum bleed solenoid to help out. That is why the idle tune up is so complex.
I had a similar gremlin.
Sometimes it would idle perfect, then for no apparent reason, start surging up to 1500, stumble , fall to 400, and surge again, sometimes stalling.
When I went to get tools & meter to start checking, it would idle perfect.
I had a big improvement show when I replaced the firewall to bell housing ground and added an alternator to body ground. If those grounds are not perfect, the ECU’s sensor grounds try to carry some of the spark & alternator load. The ECU tries to recalibrate & goes nuts.