My 2005 Mkv TDI will drive like a dream all day as long as the engine is kept running, but as soon as I switch engine off and back on, the car will misfire exactly 26 seconds after ignition. The misfire always starts exactly 26 seconds after the 2nd ignition of the day and for every ignition of the day thereafter. For example yesterday I drove it solidly for 3 hours without a problem but it misfired on each journey thereafter. This pattern repeats itself every day.

Diagnostic check throws up fault code N242 on Cylinder No3 'P1267 Regulation Range Exceeded-Intermittent' yet it can't be a mechanical fault as the car will drive perfect all day as long as ignition is left on. Is there a sensor which feeds to the ECU only on ignition?

The cylinder No:3 and its wiring loom was replaced by VW only a year ago (£850) after their own Diagnostic check threw up the exact same fault code. I am beginning to think that the cylinder and wiring loom was fine and that the fault is elsewhere but manifesting itself on Diagnostics as cylinder 3!.

I don't want to take it back to VW as they will probably argue that the work they did is fine and that the fault is elsewhere which will probs generate a massive investigation bill. I am totally baffled by the issue. Any suggestions backroomers?