Suddenly my motor (1999 F100) has started to run pretty ragged. Hard
to fire up and maintain idle and seems to only be firing on two
cylinders. Did some basic trouble shooting with my brother in law who
is an auto mechanic and here is what we come up with:
Cylinders 1 and 4 not firing properly
All spark plugs burning clean; none fouled
All plug wires generating spark
Swapped the coils and removed individual plug wires with motor idling
to see if one of the coils could be bad - negative
Doesn't seem like a fuel filter problem because motor will run at
almost full power at higher RPM's 3000 to 5000
Checked the fuses they are OK

The motor seems to have been running fine over the last couple years
with the exception of occasional blue smoke on startup.
I am planning to have it serviced soon, but most places down here are
booked for the next couple weeks. I'm wondering if you guys may be
able to shed some insight into this , seen similar occurrences or can
give me some idea of what to expect in terms of repair.