Try web search using wide band lambda sensors this may help.
These are pretty good at showing fault codes if faulty, have you any codes logged ?
What make was the after market sensor ? genuine from TPS are not that expensive.
Would be good to post 4 gas and live data if you need more help with fault.
Cheers Aidan
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Audi TT 1.8 2002 - 5 wire Lambda sensor - Fixed # - Pete Mutlow December 29, 2009, 11:56 am
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