Hi Wyn, what nelson was telling you was correct. You may very well have a faulty crankshaft position sensor but it is very important to have the fault codes read before anything is replaced. You cannot read the fault codes without a scan tool. They sell code readers like the ones here on Amazon if you want to read them yourself. Your problem will not be your air filter but it could be your air mass sensor but once again, no parts should be replaced until a diagnostic scan is performed and the faults are analyzed. Let me know if you have any questions.