I don't know anything about this, so please bear with me. There are three idle settings in the PFC (normal, electric, and a/c). When my lights are on or the a/c is on the car idles at the exact rpm that is set in the PFC. The "normal" idle, however, never idles at the setting in the PFC. It's always higher. Why would the PFC be able to control the electric and a/c settings so accurately, but not the normal setting?

Also, I've tried adusting the two idle screws and all that. The idle will hold to a good value (800-850) for a day or two then go back up to 950-1050. Thanks for any advice.

-Matt

 

Usually that means the engine is getting too much air, but you said you tried adjusting both idle screws.

Try resetting the PFC; or turn O2 idle control off, adjust
the mixture for the middle or lean side of the range, then try idle with O2 off and on.

Maybe your ISC solenoid needs cleaning. If never done, it is sure to be very dirty and maybe sticking.

 

Where do you adjust the O2 idle control? Also, what is the ISC selenoid? Is this what the PFC (or any ECU) uses to control the idle? Thanks.

 

Nevermind... I got it. It was the air-adjusting screw. I though I had it tightened, but it never truely was. I finaly took off the elbow and made sure it was tightened all the way. Idle is perfect 750.

 

Idle Speed Control = ISC.

I suggest you religiously study your Mazda maintenance manual, mainly section F. This covers all engine control systems.