I just converted my A/C to R134; the car cools down fine on all fan settings while driving. When I idle the car, if the fan is set at the lower two settings, the idle initially goes to 1000 then drops to 750 within a few seconds. However, if the fan is on the two higher settings, the idle cycles between 750 and 1500 and the car eventually stalls. Any suggestions for a fix (short of not using the A/C at the higher settings)? I'm guessing vacuum leak somewhere, but maybe ECU reset might help?

 

Could be your BAC valve. If it is dirty it will not respond very quick, causing the idle to drop or engine to stall. You can check the voltage or take it off and clean the carbon out.

 

BAC?

 

BAC Valve = Bypass Air Control Valve

Its on the intake manifold, introduces additional air to the engine when the A/C is on, power steering is being turned hard, 800 W stereo blasting, or other extra engine loads AT IDLE.

 

Mazda wants over $600 for a BAC.