Testing IAC valve on 1992 4.3 truck
 

I am working on clearing up some drivability problems on a 1992 4.3 truck with auto trans and 225K miles on it. I had engine shuddering when deaccellerating, which a new timing chain and gear fixed. I still have the problem of the engine wanting to stall, when rapidly taking my foot of the gas at low speeds, such as backing up, or driving around in a parking lot, etc. The engine idles smooth, and has no hesitation when pulling out, and drivability is otherwise great.

I suspect the IAC valve. I removed and cleaned it, and it made no difference in vehicle performance. I removed the connector plug and started the engine, and it idles much faster, which tells me it is at least partially working. I also put a can of Seafoam through it, 1/2 in the tank and the other half down the throttle body, making no immediate difference. I also replaced the coolant temp sensor unit and tested the TPS for voltage and resistances, and found it to be OK.

Is there any good way to test this IAC valve? What voltages should I see on the connector plug? Unfortunately I don't have a used spare to use as a test. Any advice would be appreciated.