Honda Element revs on its own while idiling

My 2008, standard transmission, Honda Element just turned over 100,000 miles recently. Over a year ago the engine started making a “hurrr hurrr hurrr hurrr hurrr” noise and shaking the whole car while I’m sitting at a light or stop sign without touching the gas pedal. If I turn the air on it will stop, but starts up again if I turn the air back off. It doesn’t do it all the time, and of course didn’t do it when I took it to a mechanic to have it checked out in June. They hooked it up to check for engine codes, and got nothing, so they weren’t really sure what to fix since they couldn’t make the engine do what I was describing. They did bring a whining noise the engine is making to my attention, and suggested replacing the alternator and 2 associated belts in the engine. While they were in there fixing things, they noticed the lubrication looked contaminated - like water had somehow gotten inside - but couldn’t say how.

Unfortunately, my car is pretty much right where it was before visiting the mechanic - only now I notice the constant whining that gets louder when I press the gas pedal, as well as the occasional shaking and “hurrr hurrr hurrr hurrr hurrr.” Please advise - people who ride with me notice the whining too, and whenever the engine starts shaking they think I should have it looked at. to which I reply, “yes, I have. fat lot of good it did me.”

Possible bad tensioner or idler pulley for the noise. Any decent mechanic with a stethoscope should be able to nail that down. There are two things that might be causing your idle changing without your input, IAC and TPS. They will not always set a code it they’re bad. Let me repeat that: if either of those go bad, they will not always set a CEL code. I’ve changed several and fixed idle problems without the CEL light coming on. Perhaps if they go totally dead they wil set a light, but your problem indicates the problem is only intermittent.

Poor idling of the Element means it might be time for some of the major services recommended by the mfgr at the 100K mark. Valve adjustment, cleaning the throttle body, spark plug replacement. I did these three services on my 70K Element and now get 1 mpg better in city driving. I didn’t have any issues beforehand but afterwards the car does seem to idle and run smoother.
A dirty air filter will disrupt the smooth flow of air to the engine, and may allow dust particles to reach the mass air flow sensor, further diminishing the idle quality.