Hello, 2005 Ranger XLT , 2 wheel drive, ext. cab, 4.ol V-6. Due to the cost of changing the spark plugs had a friend help me. We changed the plugs and wires both. Installed Motorcraft plugs Changed the fuel and air filter also. Now the truck will idle fine then stumble (like miss ) then idle fine then miss again. And if you set in line some where it's like the transmission kicks in . Really weird you pushing on the brake and it try's to lunge forward. Any idea's.

 

Was it doing any of this Before the plug, wire & filter change?

EDIT: Scan for trouble code clues & post All code Numbers, as they can help focus a trouble shoot.

Did you also use Motorcraft plug wires, or a quality brand that says in writing it's product meets Fords specifications for waste spark ignition systems Double work load?

The random miss sounds like a faulty, or damaged plug ceramic insulator, or faulty plug wire, or maybe a wire didn't get connected, or routed properly, or the coil pack has developed a case crack, that's causing an electrical breakdown problem/faulty/wimpy spark.

Raise the hood after dark with the engine at warm idle & look for a arcs & sparks light show. Maybe one at a time spritz the coil pack, plug wires & plug boots with a spray bottle of water to see if you can cause faulty insulation to show itself or the idle quality to change. If no joy, the coil pack is known to crack underneath & break down unseen, so raise the coil pack & spritz it under there to see if you can induce a light show.

Once you get the random misfire put right, did the lurch problem go away?

 

Thx Paw I will look everything over. No it was not doing this. It had 175,000 on those plugs and wires center electrode was burnt clear down. Fred is kind of a bull in china closet so he could have damaged something. The fun starts.

 

Good idea to recheck the work. Were these Motorcraft plug wires, or a value brand after market set?

After the Dealers lead Tech installed a new crate engine in my then new 99 4.0L, it developed a bad random miss, that one day got Really worse in a driving rainstorm while I was going up a slight grade.
With this info, they performed the "wet down test" & found a crack in the #6 plug external ceramic insulator. New plug put things right, so the misting wet down test is good for finding intermittent break down in our high voltage secondary ignition.

If a trouble code scan turns up a cylinder # misfire, it can help focus your trouble shoot.

Let us know what you find.

 

I have a 2004 with 4.0 engine that miss fired very intermittently. Turned out to be the coil.

 

Well money pit 69, how is the random misfire trouble shoot going, 145 curious minds would like to know?