I still have the 157k car, its motor is pretty far gone but I'll be installing my good spare one at some point this winter, whenever that elusive free weekend turns up... Is yours the one that was advertised on CL for the past several weeks, down in Tacoma IIRC a light blue or silver sedan with blue interior?
Regarding the engine running problems you described: Could be injectors, or they could at least be a contributing factor, but there are several other possibilities as well. One is valves -- they probably have not been adjusted in ages and may be out of spec. Misadjusted valves can also contribute towards smoke, poor starting/running, and low power. They are easy enough to check, just need a set of angled feeler gauges. If they need adjustment, that's more of a job, requiring special tools and a set of shim discs of varying thicknesses. I have all that stuff so can help out if you get to that point with it.
Make sure your glowplugs are a matched set. If you don't know what kind are in the rear 3 holes, then put in the same type you installed in the front three so they can be ruled out as a possible factor. Mismatched brands/types of glowplugs can cause all kinds of running issues, including major engine loping due to uneven compression from unequal-sized tips taking up varying amounts of volume in the combustion chamber and causing uneven engine compression. Ask me how I know.
I have had OK results with injector cleaner products in some cases -- Diesel Purge is a good one, made by Liqui Moly -- but at the end of the day injectors don't wear out just by becoming dirty. The physical metal parts themselves wear down, and running a cleaning product won't fix that. After 170k, they should be rebuilt. If you have a pop tester, then you will be able to make sure they are all matched properly and have a good spray pattern. That will help the engine run better in every way. The only time I have seen injector cleaner really help is when someone has done something dumb to their engine, such as running unfiltered and unheated veggie oil in November like happened to the poor Mercedes that got towed in a couple weeks ago. Don't do that.
If you do, BG or diesel purge will help clean up the mess, but my guess is that in your case they are just plain worn out.
Finally, here is the big one: timing. You are right that most shops had no idea what they were doing when they worked on D24T engines. Replacing a timing belt on a D24T is not a horrible job but you have to take some extra steps to make sure it gets timed right. Most shops don't take those steps -- they just slip a new belt on and don't worry about it. That causes the engine to start and run much worse. Timing would be the first thing I would check. If you don't have the tools or know-how to do it, let me know and I'll find a way to help out.
If you get your timing, glowplugs, and injectors sorted out, and assuming the engine compression is still solid, then I think you'll be much happier with the way it runs. I'm happy to give it a look-over some point; shoot me a message about setting up a time. What part of town are you in?
Local parts sources around here are tough -- at the shop we can get parts through IMC which has a good selection, other than that there's Ravenna Volvo, which I don't mind supporting, and Abe at MBMW Parts is a good guy too. There's Bow Wow in Lynnwood for VW parts, but they are not great on Volvo stuff. For Volvo body/chassis/interior items Northern European in Ballard has everything but they are not cheap and have almost no D24T stuff.
Don't forget to run sustainable biodiesel in it -- Dr. Dan's in Ballard is the place to get it. Better for the car and for the environment.
