Help for 240D injection issue?

[BoiseBenz]

My friend Oscar runs a repair shop, concentrating on MB gassers.

This particular car looks like a taxi in Beirut, but it has a three-year-old MB rebuild and a manual trans, and only 320k total miles with no rust.

Not long ago the owner's kid was driving the car, and "it suddenly quit." As it turns out, the car will start right up, but only if you floor it. Floored (or manually pulled to "full) it will run at about 1300 RPM (estimate). Gently releasing a little the car will drop to "idle" speed, and idle perfectly smooth, with no smoke or unnatural clatter--even when cold. Any lower/less it will stall. Basically, it runs like a dandy but the fuel selector seems to be set about 3500 RPM too low.

I'm suspicious that either something went haywire with the governor, or the kid was jumping it (?) and the rack skipped a few teeth. Any ideas? If it's not simple (read: "cheap"), the car will be scrapped.