Centurion

A big possiblity is that a vent needs to be adjusted. That was the case with my moms car a while ago and we took it to a mechanic who got the job done wihtin four hours without changing any parts. Shouldn't cost you more than 100 dollars.
Issues with the engine are a nightmare, especially because it gives mechanics an opportunity to gauge you bank account.

Don't forget to check the plugs.