Father-in-law type person Ed drives a 90 300D (2.5 turbo). Complained night before last that it "hasn't been able to rev over 3800 rpm for a while." Says he just "stands on it getting on the freeway, goes up to 3800 and won't rev any higher, won't shift until I let off the gas a bit."

Of course, it's dark and raining at this point..... goes well with my complete lack of experience with diesels. I poke around looking for open vacuum lines (he's got a couple that are prone to pulling off any time he goes under the hood), can't see anything obviously amiss. Start the car, idles fine, pull the throttle cable under the hood, revs up fine. Sit down, confirm rev's up well past 4k in neutral. Out for a test drive, shifts normally, revs to ~ 4500 or so before doing so if I'm pushing it. Out on the highway, all seems normal. Return the car to Ed, call it a night.

He didn't drive it yesterday. Today he did, calls me to say "won't rev past 3800 rpm again."

Any hints as to where I should start looking to trouble shoot? Guessing fuel related, if for no other reason than he's been walking the bottom of the tank for the past several weeks (well and truly cash strapped).

Thanks in advance!

__________________
1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife