RPMs jump to 2500 when clutch is disengaged or transmission put in neutral

Question

Good morning all. I drive an 05 Chevy Cavalier, 2.2L, 5-spd manual trans. Lately I've been having issues which I am told is throttle related. As I'm driving for a little bit (time varies) I go to downshift while or without braking, and my RPMs go up from say 1000 to 2500-3000. RPMs go down when I release the clutch. Now when I come to a complete stop and shift to neutral and release the clutch the RPMs go up to 2500-3000 and it takes about 5 seconds to return to a normal idle. This has been ongoing for about two weeks now.

Anyone have any ideas as to what the issue might be?

Answer 1

These are common symptoms of an split air hose allowing unmetered air into the engine intake. Check all air related hoses for cracks. Hoses include the main air intake, crank case ventilation system and vacuum hoses.

Answer 2

As @handyhowie indicated, the source of the issue is more than likely unmetered air or simply an 'air leak'

This creates what's called a 'lean condition' for your engine. When you are lean in your combustion mixture you have too much oxygen and not enough gas. The symptoms are exactly what you describe. You can also have your engine temperature increase a bit when you are experiencing a lean condition, especially in stop and go traffic.

A common culprit is a vacuum line that has detached or a crack in a vacuum line.

If you have a can of carburetor cleaner you can use tiny squirts of it around your carburetor or fuel injection throttle body to see if it drops the idle down as the liquid temporarily blocks the crack that is sucking air into the system. You might also smell it as it comes out of your exhaust. The odor is a sharp NOx smell. This is a great indicator that you have an air leak issue.