no but iirc 15.1 isnt lean it is around lambda 1 ie ideal economy, turbos need extra fuelling on boost etc with amongst other things heat, ie i assume you will see 11s on full chat,something i assume a na golf gti should never see?on a narrow band gauge and sensor lambda 1 is around the middle of the reading range, if i plumb a gauge in its off the clock lean ie 17s maybe more, basically the end of the narrowbands reading range im no expert so may be talking utter bollox so fire suit on