What are some fairly cheap upgrades i can put into my car that wont mess with it. i'm looking to get better acceleration. it is a 4cylinder. and also the check engine light is on.. anyone know what might be wrong. mechanic said its because the engine is missing something in the emissions part. i think he's just feeding me some bs. and i also have rockafosgate subs and amp i want to install with a pioneer deck. i dont know exactly how to hook it all up. if you have a good website thatd be nice thanks.