Diagnostic caps on !

[nobananas]

Got a T5 manual in at work at the moment. Failed MOT on emissions as the tester cannot get the vehicle to hold a constant RPM between 2500-3000. The revs rise and fall by 500 rpm in 5 second 'cycles'. Codes pulled say MAF fault, swapped for known good one and no change so suspected air leak. Checked all the hoses and usual suspects and also pressure tested the boost pipes from the turbo to intercooler pipework onwards but the only leak was from the intercooler drain and no leaks between the MAF and turbo.. The IAC seems to be cycling the revs up and down but I don't think it's the cause as with it clamped off it still tries to do it (only slightly less) The only thing that stops it is disconnecting the Lambda sensor, and oddly with it disconnected the emissions including the 02 readings are spot on (although the CO readings seem a little lean to me). I've never had a Lambda sensor act quite like this when it's failing, what do you guys think, any suggestions ? Also the MAF code has never reappeared.

[kyboy]

I had something similar with mine changed maf etc and that was the lambda!!

[nobananas]

Thanks Kyboy, it's always more difficult when it's a customers car as your spending their money, been robbing bits off my car and trying them all day !