Hey rotorheads,

The idle on my 90 GXL tends to flucuate the more electrical load there is on it. Putting on the AC at idle will cause it to dip enough that it dies. With no AC, radio, lights or blower, it idles fine.

TPS set with the mazdatrix tool and timing perfect.

What would cause this.

Brian

 

Sounds like your BAC valve which should compensate for electrical load at idle. Make sure the valve is clean.

 

Try unplugging your BACV, and drive around. Is there any change?

 

I tested the BAC valve and the resistence was within the specs. I swapped it out from that on another car that ran fine, drove around to warm it up, flipped on the blower and AC at idle and it died.

Any other ideas?

 

Check the voltage (DC) the BAC is getting.

At idle, with nothing on, it should be around 11-11.5 V

when you turn on the ventilation to max, it should dip to maybe 10.5 V (the actual voltage value is not that important but it should be lower than what you get at idle). Basically, the lower the voltage, the more air is allowed to go through the idle circuit.

If the voltage is not changing, something is wrong in the ECU or the cabling from ECU to BAC.

If the voltage is dropping ok, then it's gonna be a brain teaser since you are saying the BAC itself seems to be working ok. Maybe problem with alt or battery, although very doubtful since you are saying the AC load causes car to stall.

Note that that turning on the AC or turning on the blower are very different in terms of idle control. When turning on the AC, the ECU gets a signal directly from a sensor that tells it to up the idle via the BAC. When turning on the blower, headlights, rear defroster, or fog light, the ECU does not get a direct signal, it's indirect via the load put on the engine by the alt (something called the 'electric load control system' inside the ecu).

Hugues -