I had the same problem and found the same solution. Check that the microswitch and Throttle Postion Sensor both provide the idle signal. (TPS has three leads - idle, WOT, and ground. It can be tested at the connector in the harness channel above the inlet manifold.) My TPS only showed an intermittant idle signal when exercising the linkage, so I partially disassembled the linkage, including the socket joints links down low, cleaned, lubricated, and adjusted. Used white lithium grease on the socket joints under the inlet manifold and WD-40 on the roller joints above the manifold. End of problem. Took about an hour.