1998 Ford Windstar 3.0 6 cylinder has a p0174 code indicating a "lean" situation.

Question

Checked vacuum lines, wiped out MAF. While I had the MAF off and all of it's electrical connection disconnected it would start and idle fine for about 2-3 minutes then it gets rough when I go to give it gas it seems as if it's choking out so I have to feather the accelerator to keep it going. Funny thing is that it ran fine to work then when I was coming back from lunch it would not accelerate past 20 to 25 MPH, and was running extremely rough and backfiring through the plenum through the throttle body. On my way home it drove fine like it always has. Now it will start but rough idle for a couple of minutes while feathering accelerator pedal. Any suggestions are appreciated.