i was geting the lean codes weekly in my truck with the stock filterbox and k&n replacment filter. and the truck seemed to stutter horribly. i think it was my Mass airflow sensor acting up causing the lean codes aswell. and it hasnt busted a code on me since i put my col air intake on and it runs alot smoother and peppier

 

Mass air flow sensor will definitely shoot those codes. Take off. Spray good with brake cleaner. Let dry. Like new

 

You are not suppose to use brakleen on electronic sensors. Use the CRC Electronic cleaner. Brakleen has chlorine in the red cans, and the green has a chemical that melts a lot of plastics. I use the heck out of Brakleen for most everything except any sensor who sniffs. I personally don't use the green brakleen (05088) and use the red (05089). Luckily I don't have a licensed shop or I couldn't use the red. I'd be stuck with the green junk.