It started with intermittent humming from the engine. The humming can happen at any time (accelerating, in park, driving fast and slow). When I turn the car it seems to get noisier. I have noticed a burning oil smell at times. It has also begun to rev up to 2 in neutral. Lately it has driven poorly all around. Sometimes it seems to hesitate when starting and it feels rough when braking. Any suggestions?

 

Vacuum leak check the back of the intake its about 5/8 dia. mine leaked at the elbow.Iac valve is my guess When mine acted up it threw no codes made the idle go up.When it was hot it would idle all over the place.How many miles do you have?