95 1/2 ton, 305ci, high idle

[scot399]

Idles at 1500 rpm, slowly grew worse. Engine temp does not affect the idle.
Have changed temp sensor, map sensor, idle air control valve, and throttle position sensor. Have checked and double checked for vacuum leaks. PCV valve is also not faulty. No mechanical binding in throttle cable. Runs great otherwise.
Have run out of ideas.

[MT-2500]

If TBI injection
Replace TB to intake base gasket.