7.3 Idles fine, then idle goes rough

[viabill]

I posted this in the 7.3 Engine problems forum, but thought I would post it here too in case that was the wrong place.

My son's 96 7.3 PSD just started going crazy. It idles smooth for about 5 seconds after starting then it starts running very rough. It sounds like something clicks and the engine speeds up some and sounds like it's going to tear itself to pieces. You can shut it off and restart and it does the same thing, including the smooth idle for about 5 seconds.

Anyone got any ideas?? He has replaced the cam pos sensor with a new Ford part, the oil and filter has recently been changed, and the fuel filter is new.

[najaf4life]

I really have no clue about that but hopefulyl someone will be able to help you out..

[pipelayerjdh]

Have you pulled any codes?

[viabill]

pipelayer- Can't read codes, yet. Borrowing one from a friend.
I forgot to mention that the CEL comes on while it is running bad. You can speed up to ~1700 rpm and it smooths out, but you can't put a load on it or it goes rough again.

[pipelayerjdh]

let us know what codes you come up with.

[viabill]

We got several codes:
P1661
P0472
P1211

?????

[gonestrokn]

maybe this will help. I'm not a tech, maybe one will help you out. At least you can see what the codes are and what caused them. You might need a tech to translate for you.

2000 Powertrain Control System Electronics Diagnostic Guide - 1994-1997 Power Stroke FAQ

[cchase]

hey, my truck did the same exact thing, it was the passanger side under valve cover wireling harness coming loose. i do have a 99 but sounds the same.

[gonestrokn]

the 1661 code for low voltage could very well be your under valve wiring harness which caused the other codes. My truck had the same problem a while back and I had a loose connection in the passenger side wiring. Those harnesses could be causing most of your problems. If you have to replace the undervalve wiring harness you might as well replace glow plugs while your in there.

[viabill]

Thanks for the inputs!! It sounds like the under valve cover harnesses are a weak point. We'll pull the valve covers tomorrow and see what the harness looks like.
Are the harnesses expensive?