My Bronco idles at 1,300 RPM for 60 seconds after first starting cold then drops to 750 RPM in neutral. I then place the vehicle in drive & the engine goes to 1,100 RPM. If I turn the AC on in drive the idle drops back to 750 RPM. If I place the vehicle in neutral the vehicle drops back to 750 RPM also. If I put it back in drive it goes back to 1,100 RPM. There is no check engine light. I have not checked for codes. Could the Idle Air Control Valve be the problem?