Hi Scotty,
My 2008 Honda Fit’s engine is revving up and down at idle. It has only 72500 miles and a manual transmission. I’ve read it could be the spark plugs, fuel filter or air leak. Is that true?
Thanks!
Manny
Typically this is caused by vacuum leaks. The engine compensates for what it sees as excess oxygen in the exhaust via the 02 sensors by adding gas. The excess oxygen is caused by unmetered air getting into the engine. Adding gas causes the engine to revv up, which isn't being commanded by the throttle input and it lowers back down in an endless cycle.
Spray starter fluid or carburetor cleaner around your vacuum hoses and listen for idle changes. Do this on a relatively cool engine to prevent flash fires. Any idle change means you're hitting a vacuum leak.
