My 2000 Sable idles up high when starting, then the RPM's drop to like 500! on 2000 Mercury Sable

I've replaced numerous parts on this car. Plugs, wires, the coil pack on #3, IAC, MAC...but when I start it in the morning, it idles up high then drops down to about 500 RPM's and will choke out if I don't step on the gas. There is a clicking sound from time to time near the throttle body before the idle catches and revs back up. It's also sucking gas like crazy!!! The check engine light is on and says the IAC is bad even after putting on a new there a leak in the vacuum? HELP!!!

Asked by for the 2000 Mercury Sable
what code did you have? i had one like this that was blowing the fuse under the hood in fuse was causing iac to malfunction ck that and vac leaks
1 more answer , 1 more comment
sounds like a vacuum leak...especially since you say it "sucks gas like crazy". The ECU is trying to compensate for that vacuum leak by dumping fuel.
I agree with #1
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