Argh... stupid me. Four blinks seems to refer to a faulty MAF. And the presence of that code didn't surprise me, as I just described how I had tested the MAF (unplugging while engine running). Well, at least the diagnostics seem to work...

There were no other error codes (just those 4 blinks every time I scanned). I didn't reset it yet but I guess it has no effect on engine functionality...?