FOUND IT!!

A friend of a friend came and had a listen and thought it could be sucking air. He held his hand over the inlet to the throttle body and instead of cutting out the engine kept running.

This morning I set to getting the inlet manifold off to check for leaks. Didn't get as far as taking the whole thing off. After disconnecting a few plugs and pipes I took off the crankcase breather pipe- which had a 40mm split in it.

Did a temporary bodge, put it back on and hey presto everything working fine. Ticking over at about 800/900 when hot. Off to the Ford dealer tomorrow for a new hose.

Thank you for your information oldford, the sensor wasn't causing the engine to over rev but it was faulty.

Regards Nick