Emissions problem update.

UK 528 E39. Car failed twice at one testing station for 'Natural Idle Test' CO emissions, at 0.85% Today the car went to my local BMW dealer for a diagnostic check.
No faults reported by the ECU. Exhaust system was examined and was OK, so they checked the emissions as per an MOT. All emissions were well within limits. Inc 'The Natural Idle Test', which was 0.50%. A big difference to the fail figure. As nothing was done to the car since it's last failure, I'm beginning to wonder just how reliable the MOT computers are, or is it more likely to be due to the examiner not getting the engine hot enough?. How often are test station computers checked? Mike.
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How far did you drive it to the MOT station? I have failed an MOT on emissions, then gave the vehicle an 'Italian Decoke' and then it passed.
I think that you need to give it a good run first. Of course, they stick a temp gauge on it, but get it really hot first by taking it for a run down a local dual carriageway first.

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