Hey guys,
I have a 2002 ford Ranger Edge 3.0 with 111,235 miles on it. I have always had an idle issue since i bought it at 90,000 miles. The fuel pump was replaced at 105,000 after a can of starting fluid go me home from the road.

I have a check engine light issue now with a P0301 touble code. While i am driving and and abve 1500 rpm i dont feel anything. But in idle , while in park or in traffic, the engine has a really rough idle but doesn't die and the check engine light starts to blink.

I replaced the cylinder one spark plug w/a direct motorcraft brand twice. The first time i gapped it at .44 like the manual says, the second after the NAPA guy told me not to gap them becuase they already come gapped at .45. The issue still remained and i replaced the wires and ignition coil. but notihing fixed it.

Any ideas on why i cant get this idle fixed, i tried what the code book recomends but i am not sure where to move on from here. The AZ guy says to check the fuel injector with a Diode, but will that tell me anything since at 1500 rpm there is no issues?

any help will be appreciated guys.

 

have you compression tested it? or know if you have fuel going to it? 3 parts to start are air, fuel, and compression. could be an injector, or it could be a compression issue

 

What does/did the spark plug look like?

Lot of info in a used spark plug tip.

Simple injector test is to unplug coil connector, so no spark
Crank engine for a few seconds
Pull the missing cylinder spark plug and at least 1 other spark plug, compare how much fuel each has on it's tip.
A dirty injector will limit fuel flow, at idle that would cause a miss, at higher RPM it could be OK but just barely.

An intake air leak near the missing cylinder can lean out that one cylinder at idle, but it would run OK at higher RPMs

An worn out valve guide seal on that cylinders intake valve can add enough oil to foul the idle firing but it would start working at higher RPMs.
You would see this on the spark plug tip