Drive by wire problem

[numbnuts240]

We're sorting out another vehicle for sale. This time it's a 2004 explorer 4.0 sohc v6, 116k miles. Misfire in cylinders 2 and 6, new coil pack solved that. New egr solved a faulty map sensor (it's one whole unit, couldn't replace just the sensor).

The issue we're stuck on is with the drive by wire system. Key on, engine off the throttle plate opens and closes fully when the pedal is pressed. Once the engine is started, idle blows, the pedal seems to have zero effect on the throttle, and it eventually stalls.

We have a good relationship with the employees at our local advance auto, so we checked a new tps to no avail. We're at a loss as to why everything stops working once the engine is started. It doesn't help that electronics are beyond our comprehension.
Any ideas, or things to check?

Side info, I personally picked this explorer up from the Bronx and drove it back to CT. It drove fine, but the cel was on. If I floored it on the highway, the cel would eventually start flashing, and it would cut ignition until rpms dropped. After that cel would go back to solid and I had control again. When I got home, scanner informed me of the misfires.
I swapped plug wires to rule them out, but nothing changed and I was sure it was the coil since 2 and 6 share the same coil on the pack.

A couple days later, I went to drive it 1 mile to my buddy's house and thas when the throttle issue first arose. I limped it there and we changed the coil. After that is when the map sensor popped up.
I know it did a lot of sitting, months at a time, but this is crazy.

[MinisterofDOOM]

My LS8 has the same EGR/MAP issue. Got the part coming in Friday. Funny how nobody stocks AJ35 parts even when they're actually 4.6 parts.

It almost sounds like something computery is wrong. Which is a highly technical term. Car off, things work right. Car on, something might be intervening. For instance: Ford has this asinine throttle limitation when in Park or Neutral that limits revs to 3000 for some idiotic reason. Gee, nobody will EVER need to rev past 3k in Park for diagnostic reasons, right?
Might be something like that freaking out and closing the throttle. Or it could be a bad control command anywhere between the pedal sending unit, ECU (which intervenes and does magic crap because Ford throttle-by-wire isn't 1:1 but sort of "adaptive") and TPS/actuator.

Which isn't a helpful answer, but basically: it's Ford electrical so you're could spend months chasing it or you could jiggle a connector and have it go away for good.

[frapjap]

Have you tried setting it on fire?

[darylzero]

Any diagnostic codes?

Not sure if these will help but...

https://www.2carpros.com/questions/ford ... ut-in-gear




http://www.explorerforum.com/forums/ind ... le.399499/

From the link above

NOW THE MOST IMPORTANT THING! This was the missing link that finally made my engine run the way it should. It was night and day and I wouldn't have believed it if I didn't see for myself. The Aviator engine (Maybe all Ford's) is extremely picky about the reset and learning procedure. You must follow the correct procedure or you will likely have lingering issues. Another forum member (A Ford tech I think) posted a video on this a while back. I think this procedure should be done on a cold or cool engine if possible.

1. Disconnect battery
2. Jumper the positive terminal to negative cable for 10-15 minutes to fully reset the computer.
3. Reconnect battery
4. Turn off all accessories and headlights
5. Turn ignition on
6. Wait at least 10 seconds
7. Start engine. DO NOT TOUCH ACCLERATOR UNTIL STEP 11!
8. Let engine run and completely warm up at least 10-15 minutes so that it can map all the idle parameters. The R's may go up and down a little during this time while it's dialing everything in.
9. Turn on headlights and let run 1 minute
10. Turn on AC and idle 1 minute
11. Take car for a test drive but be rather gentle with it. Come to full and prolonged stops and let the idle stabilize at each stop. (Don't hinder traffic doing this though).

If you do any live troubleshooting of the engine after the reset procedure such as unplugging the IAC valve, vacuum hoses, swapping plugs, etc, the PCM will learn some bad habits again and you will likely have to redo the reset procedure. Probably it will eventually relearn correctly but I think it takes a long time. I found this out the hard way. I finally figured out that this is probably the reason my engine ran poorly after the transmission rebuilt. The battery was disconnected for a couple days and the computer was reset. No doubt the transmission shop just fired it back up and drove it out cold without following the reset/learning procedure. The PCM is factory calibrated for a NEW engine. So when new, it does not need to learn anything when reset, as everything has already been optimized. But an older engine has different performance characteristics such as lower vacuum, lower cylinder pressure, more exhaust restriction, etc. Seems that this PCM does a rather poor job of learning to make an older engine run smoothly.

EDIT:
Wanted to add a little more to this in case somebody actually reads it. I thought my idle problem was cured, but after a few days it would get worse again requiring another reset. Turns out the throttle body adjustment had been tampered with, or maybe came loose on it's own. I adjusted the base idle speed to 400-500RPM. Basically this is with the throttle plate completely closed and then back off the throttle screw a half turn so the throttle plate doesn't contact the throttle body bore. This made an amazing difference in how the engine performs. Almost completely cured the rough and erratic idle, and I picked up about 25% city fuel economy.

[numbnuts240]

i actually came across that "relearn" procedure, but it didn't mention anything about turning on the headlights or a/c. i have no codes atm because of that procedure. we haven't had it running long enough for it to set anything. hopefully i can find some time to take a look at it again this weekend.

[float_6969]

A friend that does a lot of work on Fords says to check the PCV valve. Sometimes when they go bad they cause all kinds of weird problems.

[PapaSmurf2k3]

When in doubt, add grounds.

[numbnuts240]

adding to both threads for you james

[PapaSmurf2k3]

Ugh. I hate their stupid faces.