I have a stock 01.5 with 78K. I just found out the previous owner put a K&N filter in the car. I have read that it can have a negative effect on the MAF. Should I get rid of it or is it okay to leave in the car?

 

Personally I'd ditch the thing. They don't offer much performance in our free flowing air boxes. And yes people tend to over oil them and it ruins the MAF. I've seen studies too where they show that K&N filters allow larger particles of dust/dirt to enter the engine.