Q: hi my car wil rev until 4000 rpm only, what should i chek???

Hi there, thanks for writing in. This is a difficult question to answer with the limited information provided and not being able to see the car in person. This issue could be caused by several possible problems and only a diagnosis of each area would be able to isolate the cause. This could be from low fuel pressure, a clogged fuel filter, a clogged air filter, a faulty throttle cable, carpet blocking the throttle pedal, ignition system failures, computer problems, timing belt jumped, transmission, exhaust, and the list goes on. The fuel pressure or filter or a blocked exhaust will most likely be the cause, but a complete diagnostic check will need to be performed before a diagnosis is complete. I recommend having a mechanic, like one from YourMechanic come and diagnose the issue that you’re experiencing.