One of our 07 XFs is playing up at the moment, when it’s running the revs will either drop off (but not stall) or rise rapidly (power surge) and the engine warning light comes on, (great fun when your pulling out or in a tight place), this only happens intermittantly and our local mechanic can’t find the problem (no surprise there 
) As anybody else had this problem, is it the electronics playing up, or is it just muck on a sensor?
Any useful comments will be welcome