Another APP & IVS problem: P0122 & P0221

[MB66]

Hi Guys,

Well, I am here to bring another APP & IVS issue to the table. I have done all the searching I could on the net and studied diagrams and trouble trees to best understand the problem I have. I am hoping that someone out there has experienced this very problem I am having so I dont have to do more investigative work (AKA: Vehicle dismantling) than I have to do.

Ok here goes:
Working on a 2000 Ford Excursion 4WD w/ 7.3L (170k Miles)
This is a friends Excursion I'm looking at for him. His wife complains of pedal drop out 1-2 times a day (resulting in engine return to idle). She says "About 10 seconds or so & it comes back on." I have retrieved codes P0221 & P0122 from memory. Cleared codes and have driven it for the past week while monitoring the AP & IVS Pids on scanner, I can NOT get it to duplicate. I dont know her driving habits, but I have been driving the vehicle "normally" since diesel is over $4 a gallon currently.
APP was replaced less than a year ago. From my research and testing so far on the vehicle, I have gathered that when you manually set a P0221 by interupting the IVS signal, it will not set a P0122 at the same time. Like wise, if you manually disrupt the APP sensor circuit and set a P0122, this failure will not set a P0221 as a result. Basically, these 2 codes will not set as a result of a single failure of either sensor (from my experience & testing anyway), both sensor circuits have to experience a failure to set both of these codes. My thought on this issue is that I may have a bad spot in the wiring harness where these two wires are intermitantly finding a various path (i.e.: shorting out to each other, a ground spot on the frame, etc.) They do not share the same power sources, or the same ground sources. They do however share the same wiring loom path from the accelorator pedal back to the bulkhead under the dash, same bulk head connector thru firewall, and same wiring loom path from firewall bulk head connector to PCM.

Before I go ripping into this thing, has anyone experienced this same problem with an Excursion before? I am hoping for something like "Under the dash about 1' in on the harness is a known wear point, check there." LOL, I know wishful thinking.

I did read one bulletin posting regarding a chafing spot on the Driver Side Shock tower, but initial inspection didnt expose any solid findings.