Those zetec engines are notorious for coil pack failure due to the oversized spark plug gap. it's worth sorting out misfires because extended running with a misfire does destroy the cat-and you'll need a new cat-and a new exhaust manifold and flexi section because the garage usually makes a bodge of welding the new cat in.

Thanks for the comments. I was aware of the water leak problem, and checked that first, but all was dry. I suspect the coil pack, but thought it may be a waste of money changing things without checking the fault code. It will be interesting to see if there is now a different fault code.

I wish they had spent as much time on the fault, as they did on other 'spurious' things. They couldn't even have done a road test or they would have been immediately aware it wasn't fixed. The car came back washed and vacced, and a list of things they said needed doing - brake fluid change (done by them last year), rear indicator bulbs going white (they weren't), re-gas air-con, clean/adjust back brakes, replace wipers. All this would have come to an extra £181 + vat. The car wasn't even in for a service - just for the fault. I am disappointed as I have used Polar Ford for 10 years and they have always been great.

A strange end to this saga. The car has just been returned with the fault fixed, but they weren't sure what it was! They suspected a wiring fault, and the cableforms around the top of the engine appear to have been pulled apart and taped up.

Anyway, I have just done a 40 mile drive and it didn't miss a beat. What puzzled me the most was that there was no extra charge beyond the initial diagnosis and repair charge, despite an extra 5 days spent on it.

Just as I was beginning to doubt Polar Ford in Stockport, I feel a bit better about them now - as long as the fault doesn't return!