Emissions Failure on Golf Mk3 VR6

[crasherkid29]

Hello,
I brought about 6 months ago a golf mk3 vr6, am totally in love with it, my baby!!!
I recently took it through an MOT and it failed, some minor things, but another was an emissions failure.
It failed on only 1 of the 2 emissions tests...
They replaced the Lambda sensor, but this made no difference...
It was suggested that the chip, that may have been put on it has gone slightly wrong, but am still at a loss...
Has anyone got any suggestions???

[a8 tech]

Why did they replace the lambda,most lambda probes are misdiagnosed and its normally reading incorrect because there is a vacuum leak some where or fuel pressure issue making the lambda alter the afr ratio or the cat can be defective.Try disconnecting a vac pie and see if the values alter (lean/rich) and the speed the lambda activates with a false air leak.Ask them to test the lambda and try and get some fault codes and the emmision report