a simple five minute check with a labscope will tell you exactly what is going on, provided you have someone that is somewhat competent (read: not a parts changer) operating it.

checked the CTS? is the coolant level full? whats the TPS voltage at idle, and have you done a sweep test? voltage drop test on the 2 engine grounds? checked for stray AC voltage? plugs, wires, and fuel filter aint going to fix this issue.