The problem has been on and off for around 6/9 months. I haven't had the head off and taking a guess on the previous owners i would say that it has never been off, or had any major work done. I can try the cleaning of the throttle body and resetting trick. The chain does'nt sound noisy but the Vr has 80K on the clock, having said that, it's had all the services at the right time etc. I take it your not thinking it could be an electrical fault?