Join Date: Mar 2002
Location: Austin, TX, USA
Could be the idle air control servo. Its a large pintle controlled by a stepper motor. It bypasses idle air around the throttle plates via a passage about 3/8" in diameter. It's purpose is to set idle speed and compensate for things like AC, transmission, and power steering loads. Normally, if you kick on your AC you should see the tachometer bobble a little as the IAC motor brings the idle up a couple hundred RPMs. You also should see the idle speed increased on cold starts and slowly decline as the engine warms up.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI