I have a 1999 4.0 4x4 that shows 0171 and 0302 codes and "hops" when the gas pedal is pushed.
It seems to smooth out if I floor it or let off the gas pedal momentarily. I found a large vacuum hose runnng
from the top of the engine to an "L" fitting linking it to the EGR solenoid (I Think) This hose collapses after
engine starts. Could this be part of my problems.

 

Welcome to the forum

P0302 - Misfire #2 cylinder
P0171 - Lean on Bank 1

Bank 1 is passenger side of a V6 engine(Bank 2 is drivers side)
#2 cylinder is on passenger side of Ford engine

Each bank of a V6 engine has its own O2 sensor
An O2 sensor "sees" Oxygen levels in the exhaust
Too much oxygen is translated as Lean
Too little oxygen is translated as Rich

An engine runs by mixing 14 parts air(oxygen) with 1 part gasoline and then igniting that mix to burn the gasoline with the oxygen.
If a cylinder Misfires.................no oxygen is burned, so that oxygen is dumped into the exhaust manifold and O2 sensor "sees" too much oxygen in exhaust so "lean" exhaust

Ignore P0171, focus on P0302, fix the misfire first, that is most likely causing the P0171 code

Check the spark plug in #2 see what the tip tells you about conditions inside the cylinder.
And swap spark plug with #1, just to see if spark plug is the problem, they can look fine on the outside and still not work 100%

A vacuum hose should not collapse, replace that hose
Some Vacuum hoses may feel soft but they are rigid inside, can handle up to 40" of vacuum, idling engine is only 20" of vacuum
So collapsing hose is a bad hose

 

Part # F8729E498RA no longer available. No parts store has it either

 

Not sure what it is, but if you want one then that's too bad its not available.

Not a complete Ford part # so can't help unless we know what part you need

F8 = 1998
7 is Ranger

2 is wrong, maybe should be a Z

How about F87Z-9E498-RA

Thats just an elbow, try wrecking yard or make your own

 

Thanks