Humming noise, fairly loud, coming from air cleaner housing. Don't know where it is originating from. Cleaned the housing and installed new air filter housing to no avail. Recently installed tps and isp due to inability of car to hold idle. Presently holds idle, but when humming noise is present is only about 300 rpm. Hums most all the time, even before engine has warmed.
try unplugging your iac valve. you might have to hold the idle up just a little bit when you unplug it or the car might stall. Sometimes the iac will vibrate and sound like a fog horn at idle. It will still operate but big noise at idle. Off idle it should go away.