Idle control is sometimes a numbers game and even though the truck no longer stalled I could still take a look at some numbers and see what may have caused the problem. There are some important numbers for idle control on this truck. The throttle position sensor voltage is best at 0.65-0.90 volt range and the idle air control counts should be between 10 and 24. These numbers are easy to check with a scan tool. Warm the engine fully and note the readings.
When I checked this truck I found a tps signal at 0.61 and an iac count of 125! The higher the iac count, the harder the idle control is working to maintain the rpm. In this case the iac was being commanded very high just to be able to maintain an idle of 608 rpm.
From the clues, it was likely the throttle bore would need cleaning and some slight throttle adjustment to bring the tps into range. I cleaned the throttle body first and let the engine warm before taking a look at the iac counts again. I want you to see a picture of the throttle before a cleanup. Notice how little carbon buildup it takes to limit minimum airflow and cause an idle problem.
After simply cleaning the throttle bore with some spray carburetor cleaner and a shop rag the iac counts dropped to 38. So now the iac was finding it much easier to maintain 608 rpm. The tps was still slightly low. When I adjust the minimum throttle opening it will raise the tps voltage and the iac counts should drop to compensate because the iac will have to close slightly to drop back to 608 rpm. I ended up with everything right, by the numbers!
