UPDATE: I have still been having issues with the Idle on this 94 Monty. It has again been idling at 1500 RPM, and even after 45 minutes of driving, it will still want to idle at 1500. I have replaced the IAC 3 times in the past, with various results (as discussed above).

Today I finally removed the ECM which is located behind the passenger kick-panel:



All the pin connections were in perfect condition:




Junk Yard replacement ECM on bottom: All pins on both look to be in excellent condition.



I installed the replacement ECM, and hooked the battery back up. The engine still runs at exactly 1500 RPM at Idle.....no change from the original ECM that I removed. After driving it several times on trips exceeding 30 minutes, it still idles at 1500 rpm.

I now have another thought......Can a bad coolant temp sensor also cause the ECM to cause a high idle? There are actually 4 coolant temp sensors, and I believe one of these sends the signal to the ECM while another sends the signal to the dash temp gauge. Im not sure what the other two temp sensors are for. But could a faulty one cause a high idle issue?