doof in idle

G'day, make sure you haven't got the stereo up too loud, "doof, doof"........... LOL.

Sorry, couldn't resist.

It quite amazing that writing things down frees one mind to consider nuances, tangents and odds as to which issue to start next...

double check number 1 DVH
re-bleed
re-check rockers' gap's
fuel pressure test between DVH and injector
crack & inspect injectors
compression test

HI
basically identify your cylinder and chase from there .[bleed fuel off each injector to identify the particular cylinder]

did u check compressions of cylinders wet/dry ??
[Looking for a burnt valve, poor sealing ,worn cylinder]

If the head came off the block, cylinder head valve sealing needs checking .
Worn camshaft lobes ??
Were the injector pump and injectors at least checked at a diesel shop ??[run up and checked operation ]

swampy

LC - I'd have to hazard a guess that you have a leaking valve seat - however, a partially-blocked injector can also cause noise. In general, a faulty injector will cause knocks more than a doof noise.

One always must keep in mind that it is easy for tiny particles of rust and dirt to fall into injectors, no matter how scrupulous your initial cleaning has been.
Of course, you DID clean the injector pipes and nuts down before removal, didn't you? - rather than AFTER removal, as a lot of people would tend to do.

You can check for a leaky valve by removing an injector on the suspected cylinder (or from one end of the engine, working along it, if you don't have a suspect cylinder), and by fabricating an air-tight replacement fitting, with an airline connector attached to the fitting, for the injector orifice in the head.

You then turn the engine until both valves are closed on the cylinder to be checked, lock the engine from turning, and attach a compressor airline to the fitting you have installed in the head.

Apply 100 psi (690Kpa) to the line, and any leakage past either valve will show up as air coming from an exhaust port or an inlet port.

This is an effective and proven method of finding leaking valves, and this replaces the need for a diesel compression gauge - which many people don't have anyway, and which gauge needs to read to at least 500 psi (3450Kpa), as many diesels have normal compression pressures of 325-350psi (2240-2415Kpa).

You could also have a small piece of dislodged carbon jammed in a valve seat. It's amazing how this can happen, but it does. The carbon will stay there until its hammered out, which can take some time.

However, a chunk of carbon jammed in a valve seat quite often produces a frighteningly loud knock, as well as combustion gas leakage.

Cheers, Ron.