My 93 has an idle speed at 1500rpm and if you drive even 5 feet and stop the engine idles at 2000 for about 3 minutes and then idles back to 1500. Other than the fast idle the truck runs like a scalded dog. I have checked for vacuum leaks and replaced the IAC, TPS, and the MAP sensor. I have removed the Throttle body and cleaned it good and replaced the base gasket. Nothing seemed to work. I was told to check the timing but do not know what degree to set the base advance to ( the emissions control label is missing). If anyone has had this problem or knows the solution it would be really helpful. Also does anyone know what to set the base timing to? ........... I think I might have found it........ I checked the timing and it was advanced well above 20 degrees, I reset the timing to 8 to 10 degrees and the idle came down but I do not know what the idle is because when i bypassed the ESC my tach quit working, I guess i burned it out or something.