I have a 2004 Sequoia on which I installed a K&N intake ~4 years ago.Never had any problem from the day it was installed. In late summer this year, the engine was hesitating on acceleration a little when cold. I dropped it with the mechanic who usually works on it to check it out. After a $200 bill, he said he couldn't find any issue, changed the PCV valve and cleaned the MAF sensor as said that "oiled" air filters tend to get the sensor dirty. I've read various arguments against that but thats a topic for a different discussion.... Anyhow,.. no change/improvement to function.

About a month later, I decided to perform some needed maintenance myself, prior to a long road trip hauling my boat, I performed a slightly more in-depth service: changed plugs, changed O2 sensors, changed fuel filter, drained-changed fluids, etc. Not long after, I had a trio of lights come on - Check Engine and the two VSC lights. However, I don't have the cold hesitation anymore. Running the codes on my reader indicated P0171 and P0174 indicating both banks are running too lean. I've searched all over this intake looking for a vacumn leak but no luck in finding one. Just to make sure, I went all over the air-intake double checking the tightness of clamps and I also pulled the MAF and cleaned it using MAF-specific cleaner. I reset the codes and sure enough, they came back on.

The O2 sensors I installed were not OEM but BOSCH and certainly the sensor ends look a little different but were specific to this application and fit as expected. I've wondered if the MAF sensor could have been damaged in the cleaning but I'm not getting an error code regarding it.

Does anyone have any further suggestions before I bite the bullit and take it to the toyota dealer at $80/hr? Thanks.