I have a 99 explorer 4.0 ohv with 130k. Starts and runs great. Get an occasional ck eng light. It shows codes p0171-p0174 running lean. Can't find any leaks. When I erase codes ck light stays off for a long time. It only seems to come on when it's a chilly morning here in Fla. Also a lot of dew in the air and on the car in the am. I'm gonna clean the maf. Can you point me to anything else? Thanks.

 

If nothing else, try replacing the oxygen sensor(s). They're 15 years/130kmiles old, and probably should be replaced anyway.