2004 model. It has a miss at Idle and probably through RPM range as mileage has dropped to 12 MPG. At Idle, the Tac needle moves with the miss fire. Cleaned MAF sensor. I replaced wires and plugs. Did not replace ignition coil. Is there an easy test for the coil? It has 115,000 miles on it and I do not know the maintenance history. Could a dirty fuel filter be the cause?

 

Any codes? Does the "check engine" light come on when you start it then go out?
How long have YOU owned the truck?
Real blind guesses here.
I do not know how to test our coil pack. Just for grins, start it at night and look for arcing.
You might try a dose of Techron as an injector nozzle might be dirty.
I doubt a fuel filter can cause a miss but at 115K you're at or near the end of its service life.
Upstream oxygen sensors going bad cause an immediate drop in mileage.

 

Owned the truck for 5 years.
No codes. No engine light. I've tried Techron and Sea Foam. No change.

 

Does the "Check Engine" light work ?

 

yes, check engine light works.