Thanks to you all for your suggestions. I do have the information for reading the fault code but haven't actually made up the circuit as yet. Does the ECU log the fault if it is intermittant or only if a sensor is faulty at the time you are checking the codes. I think the CPS does sound like a good candidate as the symptoms when idling are as if it doesn't know where in the cycle it is which is why I mentioned the timing. I also suspected crossfiring. I will get out and try your suggestions and let you know how I get on. Thanks again