engine revving up on 1992 Mitsubishi Diamante

whats causing my engine to rev up to 2200-2300 rpm for no apparent reason? still does it if i shut engine off and restart. then it will go back to normal,about 7to800 rpm.

2 answers
Is the check engine/service engine soon light on? If so plugging a scan tool into the diagnostic 16 pin socket under the dash will indicate where the problem lies. The problem may also be caused by a vacuum leak, defective idle speed control valve or low coolant level in the engine. Check the coolant level first.
It could be your fuel injectors are dirty and instead of spraying they are spitting my cutlass does the same thing or it could be an idle clinoid problem just lower your idle screw on the throttle body or carb.