I am the proud owner of a 20 year old Audi 100. It has done 98,000 miles and is well maintained. Over the past three years the engine has cut out on the motorway a few times at irregular intervals. All power is lost and the car sometimes restarts immediately but other times it does not and needs towing.

It has been with Audi dealers and specialists and no one has been able to eliminate the problem. Possible causes e.g. dirt in throttle housing and need to replace crank shaft sensor have been addressed. We are stuck - I really want to keep the car but an engine cut- out on a motorway is dangerous. Can you offer any advice?