Whats causing my idle to jump up and down?

[Rockale]

When my car is in park the idle goes up and down repeatedly from 800-1100. What could be causing it to do this? I know my chip needs to be re burned for the 212/212 cam the last owner put it in. Could that be the issue? or is it B/C my tps reading is a .38 3.4v@ WOT lac 55-60?

 

[Bruce Urie]

A dirty IAC can cause this problem.......take it out carefully, clean it, (carb cleaner) without moving the needle at all, reinstall.....use a new gasket. Then make sure your intake pipe to the throttle body is also clean, not gummed up with oil, etc. This worked for me, make work for you.....follow the directions on www.vortexbuicks-etc.com/ to make sure your IAC is set to specs.

Bruce '87 Grand National