While trying to figure out why my engine won't shut off when I turn the key, I noticed while poking around under the hood that both lines going into the thermo vacuum valve were disconnected. I reconnected them, and the engine would crank, but not start. I went back and disconnected them again, and the engine fired right up - unfortunately, I noticed a slight knocking sound that I'm pretty sure was not there before... any ideas what this could be? I'm new to this car and pretty new to working on cars in general so any advice is very very welcome because this does have me somewhat concerned.