Thanks Dave. I haven't dug into the green books yet, but do you know if you can simply check continuity from the temp sensor and throttle microswitch back to a pin on the ECU plug?
I had previously discounted the temp sensor thinking that failure there keeps the car in ultra rich open loop mode, which results in terrible gas mileage, something I don't think I'm experiencing.
Also, I've been thinking about the MAF. In past cars, MAF failure has resulted in pig rich running as the system abandons closed loop control and defaults to a safe fuel map. However, the LH 2.2 MAF has an adjustment screw for idle mixture, and some procedure for setting this in the green books. Could failure or misadjustment of the MAF do something to force the ECU to drive the IAC all the way open?
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