2001 tacoma code p0171

Hi, I have an 01 tacoma that is throwing a p0171 code. The code is for the mass air flow sensor. I've replaced it with a new factory Denso unit, but it still throws the code. Also, Even though the check engine light stays on, the truck runs as good as it ever has, nor has this affected the mileage. I replaced the air filter when I replaced the MAF and I just replaced the factory fuel filter with a wix unit last year. Any ideas? Any help is appreciated.
Thank you!!

 

I had a p0171 (too lean) code a month ago. For me, the Denso MAF sensor took care of it. I looked into the most common problems for the p0171 code and it was MAF, air intake leak, or a bad O2 sensor. It sounds like you cleared the code after replacing the MAF and it threw it again?