Throttle Body/Drive By Wire problem

[tito0422]

I have a 2004 Explorer with the 4.0 SOHC (2wd, 116k miles) that I am trying to get running to sell. It ran, with the cel on, when I picked it up and drove it home a bit less than 100 miles. Btw, the owner lives in Florida and left it parked in NYC to use when he came up periodically, so it did a lot of sitting and not running. Here's the sequence of events:

- During drive home, cel would flash when I floored it on the highway. I would lose all throttle response until RPM's dropped, after which I would get throttle control again. I was able to repeat this a couple more times on the way.
- I plugged in a scan tool to see what codes were causing the cel to be on and got misfires in cylinders 2 & 6. I pretty much condemned the coil pack since those two cylinders share a coil. I swapped a plug wire from a misfiring cylinder with the good one next to it to humor myself and rule out wires. nothing changed so i swapped them back and left it alone for the night.
- Went to bring it to a friends house where there's more driveway space and a level driveway to work on it. On the way there (roughly 1/2 mile) throttle response was absolute garbage. RPM's never got above 2500rpm, would not shift, and it stalled a couple of times.
- Changed the coil pack, and the misfires went away. But now we were getting a code for the MAP sensor, and the engine still would not rev past ~2500rpm. New EGR assembly and that code went away.
- Now we can't get a code to further diagnose anything, but the engine will not rev above 2500rpm, and the rpm's will start to drop if you keep the gas pedal depressed.

That's where we're at with this thing. We aren't the most electronically inclined people, so this electronic throttle and drive by wire is confusing to us.

A couple things to note:
- We did try a "relearning" procedure we came across on here which involved touching the positive and negative battery leads (disconnected from the battery of course) to no avail.
- Key on, engine off: throttle plate will open fully with the gas pedal to the floor. Once the engine is started, the plate barely opens.

We're not sure if it's an issue with the throttle body, pedal, or something in between. It just confuses me that everything would appear to be working fine, until the engine is running. Any thoughts, ideas, or suggestions?

 

[SyberTiger]

Clogged catalytic converter?

 

[imp]

@tito0422 @Syber Tiger
This may be a tough one. Limp Home Mode ("Forced Limited Power") cannot be imposed without a code thrown. The symptoms surely suggest that, though. When it happened to me, idle quality was hardly affected. Shifting became erratic and jerky, and additional indicators were illuminated: "Brake", "ABS", 4X4 HIGH flashing on and off, and a tiny Wrench illuminated. Finally, it threw "Forced Engine Idle", no throttle response at all, sat and idled only. It took me several months to iron out, everything pointed to the Throttle Body, a new one did same thing.

I would think a clogged cat would cause rich running indication, which should throw a code to that effect. But, maybe not, though a clog that bad one would think the engine is choking. If you are not certain whether your code reader is "CAN Protocol" able, find out. There are a bunch of CAN enabled codes which may not have been seen yet, including ABS. BTW, ABS Module has the ability to force limited power by itself, happened to my '04.

My Throttle Plate also seemed to work properly, KOEO, watched it as my wife depressed the gas pedal. An additional check: At rest, engine off, the position of the T.P. is held slightly cracked open, you can see it and feel it with finger pressure. It's held slightly open by a spring-plunger deal which opposes the mainspring. Every time the ignition is turned ON, the drive motor CLOSES the plate fully against that plunger, while measuring Throttle Position Sensor (TPS) output through that little bit of rotation. Any discrepancy noted, throttle use is disallowed. Check for that little movement, while someone turns the key ON. It's quick, but you can see and hear it, a click and then reopens to rest position. If you don't see it, chance of TB problem.

Cranking, the throttle plate opens wide for air, but don't try for that view as the Mass Air Sensor won't have flow through it, and other things will mess up.
imp

 

[07gtman]

@tito0422 did you check the plugs for fouling, while you have them out attach the wire to it and crank the engine to make sure you have spark to that cylinder.

 

[rrgone]

Tank of **** gas that sat for a long time? Might be plugged fuel filter, check fuel pressure. Also, clean the throttle body as 2004 had issues with sludge buildup in there, although that usually causes idle issues rather than acceleration problems.