idle tach issue

i have a 94 4.o ax-15. a couple times while i've been driving lately my idle is about 250rmps higher than normal. it kinda came and went on its own. it idles higher and stays 250rpms higher as i drive. say i'm driving 55mph in 5th gear, its normally at about 1750 rmps but it was at 2000. nothing has been changed lately. anybody have any ideas?

Any check engine light? Always look for vacuum leaks with a higher idle. Some other things to think about:

*Test your throttle position sensor.
*May as well clean the throttle body as long as you're in the area.
*Clean idle air control although as this happens at highway, unlikely to be your issue

no check engine light. i'll check for any vacuum leaks. how do you test the pcm?