Then there's one of two things. The brake light switch could be slightly out of adjustment or there's a vacuum leak. Try the coasting procedure while holding the brake pedal up with your foot.
To verify a vacuum leak, you can use a scanner to view live data and look at the "step" the Engine Computer has placed the idle speed motor at. For a good-running engine, step 32 is typical. If you find it on step 0, the relearn hasn't taken place. If you find it on a lower step, such as step 10 to 20, for example, the computer has commanded the idle speed motor to close its controlled / designed-in vacuum leak because air is sneaking in somewhere else that it has no control over, meaning a leaking vacuum hose, gasket, or part that operates on engine vacuum.
If a vacuum leak is suspected, you can pinch off various hoses to see if doing so brings the idle speed down. You can listen for the hiss of a leak, or you can spray water over the engine to see if it gets sucked in somewhere.
Erratic idle speed can also be caused by the air passage the idle speed motor controls getting plugged with carbon, but that is very uncommon now with the better additives in today's gas. You need to unbolt and remove the idle speed motor to look in the passage to see if it's clear. You'll need a high-quality Torx bit for the two screws because they have thread lock sealant on them and they turn out very hard. You don't want to round out those heads.
Tuesday, October 7th, 2014 AT 12:03 AM