Thanks for the advice. I have everything you mentioned. I've heard of a leak down test but never knew exactly what it was. Now I do. I performed the test and found that the valve did not leak. I was surprised at the amount of air that came out of the PCV hole in the valve cover. I tried the same test on the #2 cylinder and got similar results but with much less air flowing past the piston. I'm thinking that cranking the engine to get the valves closed for the second test, got oil up on the cylinder improving the rings seal.

As long I was pretty much set up to do a compression test, I compared the #1 and #2 cylinders. Both read just under 400 PSI. Earlier this year I ran a compression test and got similar readings on all 6 cylinders. I think I can assume my rough idle is not due to poor compression in one or more cylinders.

I'm currently replacing the injector lines (one developed a leak from abrasion and others are worn) and as long as I have it torn down this far I've pulled the injectors and will have them inspected and cleaned at a local diesel injector service shop. I should have it put back together by the weekend.

I'm hoping this will cure the extremely rough idle.

Thanks again for your advice.