sounds like a bad iac motor(idle air control) or vacuum leak
Year? Replace ECTS and clean the throttle body
throttle posistion sensor or vacuum leak
replace the thing its faulty dont try do fix something you dont understand
On my Chevy truck it idles high when its low on antifreeze but if its not that more than likely its usually a vacuum line loose or cracked. good luck.
vacuum leak
What type and weight of oil are you using in your engine, and how many miles are on it?
see previous answers, but if it idles high it might be the Mass Airflow Sensor. if your car idles too high for too long and you keep driving it, you could burn out the transmission module (very expensive )
zyou tps might be bad
where is the i.a.c in a mercury muntaineer 2002
you might have pulled a vacuum hose off
Manual or automatic transmission?
depending on the year some impalas have 6 inch glasspacks