Hi Aidan,

When I have a running problem with a vehicle, I like to have a full picture of what is happening and when I have that in front of me, I can make a considered decision on what step to take next. Part of that picture would be an exhaust emission test at idle through to fast idle. This might show something which will give you a clue on what direction to take next. An MOT emission pass will not show up high HC's or 02 at idle for instance. I would also want to do a compression test in case of an engine problem. Also, is this engine breathing heavily?

It is very difficult to replicate this problem in a workshop so I would want to have all the facts in front of me before I start spending money on expensive parts.

Finally, to give me breathing space and have a re-think, I would be tempted to try Forte treatment on it if its breathing heavily or at least stick some injector cleaner in it and see if there is an improvement - and go from there.

Best of luck

Pete M