I replaced the spin on filter. it is strange that the tac only goes to 3k with the pedal floored in neutral. does anybody know about this symptom? it is a friends car.

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81 300sd 81 300td 87 300dt

How about the pre-filter or the strainer in the tank. I agree that that is pretty odd, usually they will still rev up with no load with a fuel restriction....perhaps it has an IP problem or something. Check the other fuel filters/strainer first.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Check the linkage to the injection pump. Make positive the arm on the pump is being advanced all the way. May take two people to do it properly. a solid indication is the first part of the pedal throw does nothing.

More information is needed.

What was the condition of the vehicle prior to the filter change? Was it operating normally? Confirm that only a filter change was done, and the symptom appeared immediately after that filter change..............

It does not sound like a condition that can develop strictly from a change in the secondary filter..........unless there is a significant air leak in the housing.

Remove the intake boot at the turbo and try running the engine. If it then revs normally, remove mouse nest , rag , PO's arm or whatever may be blocking the intake/filter. Many turbos suck in so much dust that the filter can plug solid (my 300TD wagon case in point)

Take out the drivers side carpet and see if it revs. The carpets hang up the throttle linkage all the time and don't allow the throttle to engage to full stop.