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High HCs means un burned fuel ie it runs rich at idle. Could be a egr valve partially stuck open. (it should be 100% closed at idle) could be worn out injector nozzles, could also be a sticky iac (idle air control) motor. But probably not a computer problem.
Did you have it diagnosed by a scanner of some time? Sounds like you are pulling/replace instead of diagnosing the issue prior to fixing. You probably have a bad IAC sensor, but it could also be the throttle position sensor. Do have a check engine light when it does run? How many miles are on the vehicle. it could be a timing issue. I had a 95 Lumina and it turned out to be a sensor, but mileage does play a key in this issue.
Zab, First things first, check for any vacuum leaks, hoses that are disconnected, cracked or just plain worn out. Also check for vacuum leaks around the throttle body.
It really sounds like you have an EGR valve that is stuck open ever so slightly. The MAP sensor is a result of a low manifold vacuum. The IAC (idle air control) motor is trying to compesate and keep the engine running resulting in the high idle speed. I would remove the EGR valve and clean it gently with a brush and pick to remove any carbon build up.
Let me know, regards.