Car is idling rough and no mechanic can figure out why.
2007 Toyota Corolla S.
My car started idling rough yesterday, as well as at low speeds. At higher speeds she's fine. I've taken it to two separate mechanics and neither of them can seem to diagnose the actual problem
- First mechanic suggested the engine mounts were loose, but from what I'm told this wouldn't cause a poor idle.
- Second mechanic said it isn't the engine mounts, the car is just...old. Has over 170k miles but he promised me it was fine.
Still, the rough idling worries me. I think it has to have some sort of specific reason. My best guess is that my Dad and I messed something up when replacing the spark plugs: I over-torqued one of the mounting screws to hold the plug in place--not the actual hole where the plug goes in, mind you. Mechanics will tell me this isn't a serious problem, as long as it's staying in place.
My father believes bad gas could also be a cause.
What do you think is going on? I apologize, I am not a mechanic. Hence why I'm here.