I did already add injector cleaner and have driven it about 20 miles, but no difference yet.

However, a bit of a breakthrough on the diagnosis. Although I had already done this, I was probably in a bit of a hurry earlier and missed it. When I pull the boots on the plugs one by one, they all make a change in how the vehicle runs except for cyl 5 - I can hear no difference when I pull it off of the plug. I know the cylinder has good compression (thankfully), and I see a big fat spark as I am pulling that plug wire out of the socket, and have confirmed that the wire is firing with a timing gun too. So....my conclusion is that this injector on the cylinder is not working. Is this the correct conclusion? Could it be a fuel pump issue on that one cylinder, or is it pretty safe to conclude it is the injector? Aside from installing a new injector, what can I do? Should I remove it and try to clean it?

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K