MOT FAIL!!! CO2 at Idle? - Help!!

My lovely 1999 S70 just failed on emissions -CO2 at idle should be less than 0.5% but is actually 1.83%. Strangely, at fast idle it drops to 0.07%. Does anyone know what could be wrong? The car drives perfectly, idles smoothly, never cuts out, pulls strongly etc.... I have no warning lights on, a full service history and 96k on the clock. Also the car was checked for fault codes about 3 months ago at the last service. Any advice would be appreciated - I will have a hard time getting it in for diagnostics any time soon and with Christmas comming up that will delay things further.

It means the mixture is too rich at idle, it would be good to be able to measure short term and long term fuel trim. But my best guess is an induction air leak, check all the vacuum hoses and induction pipework for holes/splits. Is this a turbo model?

Its the non-turbo 20v engine. One of the late spec 'classic' shape engines with variable valve timing. I will check the vac pipes as soon as it stops raining! As for the fuel trim - I have absolutly no idea what you are talking about!?! Incidently, I have just checked last years MOT slip and the natural idle co2 was 0.253% so very low.

Thanks, by the looks of that I'll need some good diagnostics kit to investigate trim. I'll start with the vac hoses, then I should be able to get the car into Volsaa engineering on the 23/12 so they can look deeper. Hopefully I can get it fixed before then though because that won't give me enough time to get the car back for its free re-test.

My 96 850 t5 suffered with this at last mot and was advised to put forte aditive into it after that it flew through and is guaranteed for the full year but can only be bought though a garage its not available to general public

Forte 

Hi, i have always worked with cars, and i know of a couple of places that sell forte to the public around the motherwell / hamilton area. regards stuart

Forte - not available to the public - so it must be on ebay right? :) Is this the stuff? James

Update.... Checked for vac leaks, but couldn't find any. Took the car down to Volsaa (a place local to me with a good reputation) who plugged it into their equipment and found NO error codes at all. They couldn't find vac leaks either, but said they didn't think that would be the problem because other emissions readings were nicely in limits. They then changed the air filter and plugs (apparently the Bosch which were fitted are not liked by this engine). They have also tried 2 new Lamda sensors. They have tried disconnecting the battery to reset the ECU - but still no good - in fact the co2 has now gone UP to 5% !!! They haven't run the Forte through it yet (though they do have it on the shelf). I changed the MAF about 7 months ago due to an irratic idle and an error code suggesting the MAF was no good. Nothing changed so I tried cleaning the ETM, which did the trick. I still have the old MAF, so tomorrow they will try that. The bill is going up but the emissions aren't going down!! Anyone got any more ideas please?

Suggest that the fuel pressure is checked at idle and fast idle to confirm the fuel pressure regulator is functioning.