This is not a question, I want to get my experience written down to help the next guy (probably 5 years from now searching for it).

Left the lights on and ran the battery down on our '05 F-250, 5.4L. Charge the battery, it starts fine, no problem; but when I go to pull away, there is no throttle response. It will only idle. (You'll see later when I reveal the issue that the battery couldn't have anything to do with causing limp mode, but that is when the problem started. No idea why.)

So I pull the codes. I get:

P2111 Throttle actuator control system - stuck open
P2104 Throttle actuator control system - forced idle

I do some Google Fu and the consensus seems to be the TPS is bad, and the computer thinks the butterfly is stuck open. Seems reasonable, so I (actually the boss, thankfully) spends $112 on a non-returnable Motorcraft TPS. Gotta get the good parts, you know.

No change, as you can probably guess. This time I noticed that I could hear the throttle control motor moving, and it was very rattley sounding. This is during a key on engine off scenario. I could even see the "absolute throttle position" parameter changing on the Scantool. So the TPS is good for sure, and the motor is moving the butterfly. But as soon as the engine is started, the butterfly is held closed and we return to limp mode.

Well the motor is awfully rattley sounding. Almost sounds like stripped gears. I decide to take the motor assembly apart to see what's up, and the cause of all of this is immediately obvious: the torsion spring that closes the throttle plate is broken. So P2111 was right that the plate was stuck open, and it was not bad data from a faulty sensor. Does anybody sell the spring? You're joking, right? We could have searched junkyards for the spring but 1. a used spring will be likely to break just the same, 2. junkyard will likely want you to buy a complete throttle body thus lessening the price advantage, 3. didn't have time to mess with it anyway. But a complete throttle body from NAPA did resolve the issue 100%. I have decided that the rattley, grinding gears sound was a jumpy throttle plate, bouncing back and forth while trying to hold a position since the motor is not getting the resistance it expects.



So if you're looking at the same problem, pop the cap off of the side of the TB motor. Round, approx 1-1/2", pops off with a screwdriver. You should be able to determine if the spring is loose or if it has a proper amount of tension without taking the whole TB off like I did. Good luck.

 

Perhaps this discovery would make a good addition to the tech folder here?

Very informative and interesting---thanks for sharing your findings!