idle's weird

Lately, my car idles at 1500 RPM ALL THE TIME… it’s supposed to idle at 600 RPM. And I see black suit on the exhaust and bumper. I know my car burns oil, but it’s never been dirty like that. (exhaust). And sometimes, the car hesitates (only when cold).
Don’t know what to do… Should I leave it like that or should I try and fix it?

could be IACV or tw sensor. check those sensors out.


Can enyone tell me where the IACV Sensor is situsted under the hood?(SPECIFICALLY)