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Originally Posted by ShawnZR-1
Question: Why does it only do it until the speed goes below a certain MPH? It seems to settle down around 5 MPH and if I blip the throttle when I'm not moving, the idle drops like a rock right to the set idle RPM and doesn't dip at all.
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The idle air PID control takes over at 5 mph to control the idle speed.
While it is tempting to go in and start changing the calibration, such as has been suggested here, I honestly don't think that is the solution. GM didn't miss the tune on 6000 cars, and they all don't surge. Some things to check...
1) if the condition exists only with the modified cal, is the spark advance smooth in the region of low load, low rpm? Has the closed throttle advance been increased?
2) check the MAP hose for contamination. When I had this condition, the MAP reading at coast down was fluctuating wildly, and causing the surge.
3) if you still suspect the IAC movement is responsible, try to reset the IAC motor as outlined in the service manual.
Todd