04 6.0 running problems

[BC1954]

I bought this 04 E-450 box truck new. Started having intermitent problems at 400 miles. Ford replaced 3 turbo's, 2 EGR's, reflashed numerous times, even installed flight recorder for a week. Never sets a code. It runs fine then just starts with a loping idle then idles normal. At highway speed will raise RPM 3-500. All new filters. No water in fuel separater. Just replaced ICP. Worked great for about two weeks. Now doing it again. Still intermittant. Saw a thread where they removed harness from ICP. Did that today. Runs great. Engine light on. Does anyone know what longterm effect of leaving that off will be? Or has anyone found a solution to this problem? Thanks!