Thank you for the insight. I'm dealing with this very problem...lean/rich p0171/p0174.
Plugs changed, all except mass flow changed in ee system. Can't find vaccum leaks.Runs half way decent at start up then misses forever. Fuel pressure at idle is just about 10# then increase idle is 27#. I have a 97 4.0. 180890 miles,nothing special except it still runs good up until now.
all during colder conditions..in the morning starting and idle was rough. Charlotte, NC
Just recently Ford installed a fuse between brake and cruise control device(which has never worked) But I don't think it has a connection to this but maybe. If cruise control trying to operate?
Any help would be appreciated.

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1997 Ford Ranger,Super Cab(full of stuff).4.0.
Nice truck ,no modifications, just trying to keep it running for a long time. 180809 miles.