1988 GMC S-15 Pickup High Idle Problem

I have a 1988 GMC S-15 pickup, 2.5L engine and it idles high. It is not a vacuum leak, bad gasket, stuck IAC, or a TPS. I have plugged in several different DTC readers, and I cannot get anything out of them, even tried the old paperclip to maybe get the check engine light to flash, and that didn't work. The truck used to just idle high every now and then, but now it has been doing it for the last few days. Hopefully someone out there can help me solve this problem before my clutch burns out. Any help will be great.

:confused: Jeff