I just bought a second-hand 2004 Toyota Corolla and I am worried it's a lemon. When idling the revs start to lower and it feels like the engine is going to stop, then there is a loud clicking noise and the revs increase. Is this normal?
No, it’s not normal, but it doesn’t mean it’s a lemon. It might only be a minor problem, so have a mechanic check it for you.