Did the mechanic check the timing of the IP? New lines can introduce air into the system. Was the return lines changed as well? If not they can introduce air into the system as well. Air intrusion in a diesel will cause a miss. If it is missing, you can crack each injector line one at a time with the engine running and listen for a change in the sound of the engine. Kind of like a gasser with spark plugs. If the IP has over 150,000 miles on it, it is probably getting tired. Is there any white smoke, black smoke, any smoke at idle? The slight vibration at idle leads me to timing maybe to advanced or to retarded. Timing an IP is kind of like a distrubtor on a gasser. Rotating it will adjust when each cylinder fires for a fine tuning. 7.3L IDI are by design a loud and clanky engine. Air intrusion is a big problem for the 7.3L IDI. I would for sure start there. Check all the return caps an the injectors for hard brittle lines and caps or fuel leaks at the caps. Just because they are not leaking fuel does not mean it is not sucking air. If it sits for a couple days and takes a while to start after sitting it is loosing prime due to sucking in air. I know this was long an drawn out but wanted to try and hit on everything that would cause a rough idle. Maybe some else will chime in with more knowledge than me.
Thanks for the detailed reply! This forum is great.
No, didn't check the timing. That was my first thought. I have been meaning to try that one myself. (I really should have installed the new lines myself; but I had a break down and towed to the shop, so I just let them do it).
Black smoke at idle. It also smokes up pretty good at high load, e.g. going up a steep grade in 4th at ~2350 rpm...
I replaced all the return caps, injectors, and glowplugs myself. It took me a while (two return cap/line sets) to get it right (I think).
The sounds really didn't change after changing all this out. I have a video from when I first got it, and it sounded about the same then as it does now. To me, this points to timing...
It was getting about 11mpg before replacing fuel lines. I am waiting to refill to know if that has changed materially.
