Maf sensor?
 

I recently got a cel code for bad Maf witch I think it was due to not being an OEM part cel light goes away after couple days then returns again I also noticed a strong thud when slowing down from around 40mph it's feels like I'm getting bumped from behind npi I put in OEM Maf sensor cleared codes and haven't felt thud in a day or so.. it's is never steady but when it happendds it's scary I hope it's not tranny any help pleeeeease

NEVER use an aftermarket/non OE Branded MAF. It has very adverse effects and can toss the transmission into limp mode. How do I know, because I tried the shortcut to the ebay maf's on two occasions. Sticking with the OE works and never an issue.

Yea
 

Like guy below me said if it's not OEM maf sensor that could be issue e bay and Amazon sells them if it doesn't say Audi and vw on it dnt use I just got one from p@p junkyard 20 bucks also baught cleaner works wonderfull