In the nine or so years I've owned this machine not once has there ever been a check engine light occurrence. Now that it's on the market the light comes on after initial start and a few minutes of idle time. At the same instant the light shows up the cooling fan starts even though coolant temperature is nowhere near what it takes to start the fan. Probed the ECM and retrieved code 35 (idle speed error).
There are no other performance issues with the engine. It runs just fine when driven.
Replaced the coolant sensor thinking that it was surely the culprit. No change.
Read the voltage on the IAT sensor and noted that it was half what the service manual said it should be. Replaced sensor. No change.
Read throttle position sensor voltage. It was dead on. Don't believe the throttle plate or the linkage is sticking.
Checked canister purge solenoid for leakage. OK. Disconnected purge solenoid. Made no change.
Checked vacuum side of fuel regulator. Tight.
Made sure the HVAC control unit input to the computer wasn't asking for AC. It was not.
Have cleaned the IAC but did not replace it. It's a little pricey compared to the other sensors just replaced.
The IAC and the computer are my two top suspects at this time. Can you think of anything else I can check before going down the road to replacing them?