What would cause the engine to idle high when started in afternoon? on 2002 Ford Ranger

Engine idles high around 2,000RPM's when started in afternoon but as soon as put in drive it drops down to 1,000RPM's?

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1 answer 2 comments
After the engine is warm, does it idle ok in park?
Yea once it was up for like a half hour or more.
Suspect idle air control. Scan test needed by a mechanic, not just codes read at parts store.