I put a K&N FIPK on my 4runner the other day and notice alittle hesitation when I ran it right afterwards. Then after driving for about ten miles the check engine light came on. I thought it could be a vacuum leak but I can't find one anywhere. One of my friends said it could the the fuel filter but that just didn't sound right to me. Anyone have any ideas?
Thanks

Try and get the code(s) from your CEL at Autozone or somewhere.

I know alot of times after installing the K & N garbage, the oil will foul up the MAF(mass air flow) sensor. This is likely your culprit. Buy some electrical sensor safe cleaner and see if that works. And as Brian said, pull the codes....they will always tell! Good luck!

Can you tell me what the fix on your 4runner.
thanks

I would guess he got a P0171 error from having a contaminated MAF meter. Oil-whetted filters (like the K&N) can contaminate the MAF if they are not oiled correctly.

In this case, the fix would be to remove the air-cleaner box and throughly clean the MAF meter with an electronic component cleaner spray.