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There are a number of things that could be the cause of this problem. Assume that plugs, wires. cap, rotor are in good shape. Also assume you cleaned the throttle body. Idle a bit higher and a richer mixture after cold start for a short time is initiated by the coolant temp sensor (not the one for the guage). Idle speed is not adjustable on your car but rather is controlled by the idle air motor. It should idle at 750rpm and 900 with AC turned on.
Contrary to some beliefs that screw is not for idle speed but rather is set to allow throttle lingage to sit at home position and the butterfly to be completely closed with no strain on the linkage. TPS switch will also be transferred or clicked at this point. Idle air is now supplied by an internal air bypass (set by the black knurled screw) and the idle air motor under control of the ECU.
I think you may have a problem with the idle air control. There are ways to test this. Have you read over the 700/900 FAQ on this subject?
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