C5 juddering/misfiring

[PaulC5]

Yesterday when on the A46 in Lincoln around 60 mph, the C5 started to judder / misfire. It was in all gears but at low speeds and tick over it was ok. It did not break down so I finished the trip (to the dealer to drop off our other car 308 for servicing) and then on the way back it was the same. Whilst there I booked the C5 in for a diagnostic in a couple of weeks but would be interested if anyone has any thoughts. The fuel level was a bit low about 10 litres so I put in another 20 litres once near home but do not know yet if this will help. This fuel had been there since last October since the car has not been used much.

It did this 2 years ago on the A1 at around the same speed but only lasted a few miles. Then I replaced the diesel filter but I took it apart and it seemed clean and no water drained out of the filter. I have a basic code reader with live data and the MAP sensor was not responding well and was bunged up with oil so I replaced it with a Delphi one. I also fit a new MAF sensor but the old one was still ok. Since then the car has done about 1200 miles.

For some time when warming up there is a temperature band where the tick over is a bit rough but when cold and warm it is ok. Over many years it occasionally gives a fault code P0299 F36 but I thought the new MAP sensor had fixed this except the code was found to be stored again yesterday but the engine light has never come on (it does light up before starting the engine and then goes off). There were no other codes yesterday when I checked.

Car details, C5 2.2 hdi 2007, 40700 miles, servicing up to date, vin VF7**************[VIN obfuscated, can be read by forum staff]

[PaulC5]

Before the diagnostic I did some more checks. I drained the fuel filter, the diesel was clean and no signs of water. Running on the drive a new code popped up but the MIL did not come on - P0104 (flow meter signal - open circuit, short circuit to positive or to earth of the sensor supply or the signal). The MAF sensor wiring looked ok but I could not see the section in the fuse box, its connector looked ok and after deleting the code and waggling the wiring it did not come back until on a short test drive. Again the MIL did not come on. I deleted it again, replaced the MAF with one I had removed 2 years before which I knew to be ok and the code did not come back.

Today it had the diagnostic and test drive at the dealer, it did not judder and they did not find anything. It also passed their car health check so nothing else obvious needs doing. I do not think the MAF had anything to do with the juddering and for now I can only suspect the juddering may have been poor fuel so I will have to see how it gets on with more use.