Please tell me if these symptoms mean that my IAC is bad. If I ground the test point to set base idle I have to turn the black screw about halfway out to reach 700 RPMs. When I release the test point idle does not go up a few RPMs. It goes to about 2000! I have to turn the screw all the way in to get the idle down to about 1000 so I can atleast drive the car.

Items replaced and quantities available for diagnostic swapping: IAC(4)(I don't really trust any of them right now though); distributor(4); AMM(3); TB & TPS(3); main fuel pump(3); tank pump(2); coil(3); cap & rotor(3); plug wires(3); FPR(3); injectors(16); fuel relays(6); ECUs 544(1), 511(2); ETC(3); Knock Sensors(3)

The only reason I've listed everything is to demonstrate the pool of parts I have available for my shadetree diagnostics. I have doubts about ALL of my IACs. Two are 540s and two are 501s. All of them demonstrate eratic idle fluctuations. Im just not sure if it is the IAC or some other factor. I don't want to buy a new IAC only to find out that one of my used units was just as good. I have opened two of them. One had the typical wear grooves in the actuator but the other one (a "new-looking" 540) looked brand new inside. It moves freely and opens and closes quickly and fully with 12 volts.

The engine and engine compartment are immaculately cleaned. I have rewired and rerouted ALL of my underhood harness. I spliced everything with solder and shrink tubing. No wires are crossed and all of my connections are A+. The TB plate and TPS are adjusted properly. Have not checked timing belt alignment marks yet but car runs like a top when it's in the right mood so I figure it probably hasn't slipped.I run my timing about 15 degrees BTDC. Plugs are Bosch Platinum. New battery and voltage regulator.

Things that I KNOW are working: Hall sensor, ECT, Fuel pumps, FPR, TPS, COIL, ECU, AMM, and voltage regulator.