LATELY WHEN I START MY MATRIX THE ENGIN RPM JUMPS TO 1800 RPM AND WONT IDEL DOWN

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WHEN I TAPE THE GAS PEDLE UNTIL PUT THE CAR IN GEAR. ALSO WHEN THE ENGIN IS WARM AND REMOVE MY FOOT FROM THE GAS IT DOES NOT WANT SLOW DOWH. BUT ONCE I APPLY THE BRAKES IT WILL DROP THE RPMS DOWN TO 1000 RPM'S I THINK THE IAC IS HANGING UP AND NEEDS TO BE CLEANED. ALSO WHEN THE THROTTLE BODY IS CLEANED IS THE IAC CLEANED AT THE SAME TIME. AND DO YOU HAF TO HAVE DIAGNOSTIC DONE FIRST