yesterday came to me one of my very first customers - I did RomDrop remap may 2021 - to check is everything still right. And we found it was NOT

at first car was running more or less ok but I found its running VERY LEAN at WOT. Lambda like 0,95 midrange 0.9 redline. How it was possible - I was targeting 0,85/0.82 ??!!

Maximum MAF reading was 140g/s - not impressive for cammed 2.5 engine

I decided to swap MAF sensor for known good one (although used). And that was it! ;-D Lambda came into place, max MAF reading increased to 160g/s what is expected 🙂

Whole thing was tricky because there were NO OTHER SYMPTOMS anything is wrong. CL fuel trims at low range looked normal, around -5% as I set. Higher load trims were slightly off (+8%) but as we see not enough to compensate WOT

mk3 NC ECU is pretty intelligent, came to safer spark advance maps so engine was not knocking but surely it was not optimal

fortunately we found it and engine is safe again and pulling strong as it should! 😃

my theory why it happened: wet KN air filter. It has to be lubricated after cleaning - and MAF sensor does not like any oil - especially excess of it!