Any Help Please!! Apologies for a long entry but I wanted to give as much info as possible.

I've had the C5 for 2 years. It's been a good car. In France this year, during a particularly hot spell, the engine suddenly started hunting. One second at walking pace then suddenly a great burst of acceleration then slow again. The engine management light came on on the dash. The RAC arranged for it to go to a large Citroen dealer who diagnosed the problem as the accelerator pedal potentiometer and promptly changed the pedal. I picked the car up and the problem returned within 10 miles.

The garage had other ideas what it could be but had an attitude ( which seems the same for the UK Citroen dealers ) of suggesting a number of options and proceeding by 'fixing' each one until the right one is hit! A very expensive method and also I could not stay in France that long for them to try. Brought home on a transporter!. The diagnostics do not seem to even come close to suggesting the right answer just a long list of possibilities.

I have analysed the problem myself and find that hot weather brings on the problem quicker as does sitting in traffic. The engine cooling is spot on but it seems to be an electronic component under the bonnet which breaks down when its temperature rises. If I leave the bonnet on the catch allowing an increased airflow it delays the onset of the problemor improvesit if it has already started.

I have been on a 75 mile trip today to check some further work I have done on it and seemed to have solved it as there was no problem during the entire journey. However when I got stuck in traffic near to my destination it started up again.

As I said the accelerator pedal has been replaced. I have checked and cleaned all EMC connections. I have replaced, with new, the oil and oil filter, the fuel filter, the air filter and the Mass airflow meter. The latter did definitely improve performance but alas after 75 miles and a traffic jam the problem resurfaced.

What could it be? I'm stumped what to try next.

Thank you for naything which could help.