That's exactly what I plan to do next. I hadn't suspected the coils, because I'm not getting a code related to them, and I was careful handling them when I removed them for the VCG replacement, but the engine does have over 120K on it, and a mechanic I know told me coils are the most common cause of misfire problems in these engines. I also thought (possibly erroneously) that the sequence of the codes I'm getting implies the injector circuits are the root cause of my problem, but maybe not.

At one time I had a misfire with fuel cut off and it turned out to be the coil, but I didn't get the open injector circuit code.

Because you have the injector open circuit I believe the misfire is from a failure for the injectors to fire. Injector not opening means no gas to the cylinders, no gas to the cylinder means the rpm when those cylinders are suppose to fire mean no increase or sustain rpm, but a decrease in the rpm which the DME detect as a misfire.

A bad coil will not throw up a code for bad coil, you will just get the code misfire with fuel cutoff, you will need to still determine what caused the misfire.

So if a bad coil won't throw a code, it is possible that I just happen to have a pair of bad coils, and the DME is shutting off the signal to open the injectors to prevent fuel from going into cylinders that aren't firing properly. Kind of strange that two coils would suddenly and simultaneously fail, but I suppose stranger things have happened. Easy to check, anyway.

You can check but like I said you also have a injector circuit open code so I would lean more toward the fact that you might have yanked a couple of wires off the connectors or broken a couple of wires in your attempt to remove the box.

Yes, that's high on my list of theories as well. I haven't seen anything yet, but I'll keep looking.

Well, I can rule out the coils. I swapped coils 5 and 8, cleared the codes, fired it up, let it idle for maybe two minutes (ran horribly, as before), shut it off, read the codes again, and got the same two open injector circuit codes for cylinders 7 and 8. I don’t know if this means anything, but the SES light doesn’t actually come on until I drive the car a little bit, which I didn’t do tonight, and coincidentally the other three codes shown in post #8 didn’t appear this time. Oh, well, I guess the coil idea was a long shot.

I spent some time inspecting the wires leading to the backs of the injector connectors, and they look perfect - they's not loose, and they don't show any sign of cracking or fraying. Sigh - I was hoping I could get the X5 running by the time my daughter comes home from college for winter break on Thursday so she can use it while she's home, but the likelihood of that looks very dim at the moment, as I'm running very low on ideas. This is quickly climbing to the top of my list of most frustrating car issues I've ever dealt with...