Misfire at idle only....
Alright, folks. I'm new to this Ranger (it's my Dad's)....I had one a few years back that was bagged and body dropped. Loved it, but had to sell before the Navy transferred me from Washington to Connecticut. Anyways, on to my issue.....
2001 Ranger 4x4 with 4.0L, almost 120K miles. Truck has been great for my Dad, and being in CT, it is used heavily in the snow. He has done all of the maintenance as required, and oil changed every 3000 miles. For some reason, his truck is misfiring at idle, but only at idle. When he first mentioned the CEL, I took my code reader over.
P0300 - Multiple Misfire
P0171 - Bank 1 Lean
P0174 - Bank 2 Lean
So I decided to start with plugs and wires. Misfire is still present. Changed both downstream O2 sensors, the coil, throttle position sensor, crank shaft sensor, cleaned the throttle-body, K&N, IAC. Still rough at idle. Friend works at Advanced Auto Parts. He let me plug in a new MAF, but didn't change anything. New IAC, nothing changed.
I've been into cars for a long time, and know enough to hold my own, but I am honestly out of ideas for this thing. IAC was my first thought, because it happens at idle only, but thinking about it, the IAC doesn't really do anything once the engine is warmed up, and the misfire gets way worse once warmed. My next thought is that it's something fuel related?? Pressure regulator, or dirty fuel filter (was changed about 25K miles ago as well)....maybe an ECM issue?? I don't know...