Los of power after deceleration

Hello disco-experts, i`m driving a 1995 tdi [2,5 L ] in belgium wich has got a strange problem for the last week.

If driving with some speed/rev`s [80 KM/3500 rpm] and then i take my foot of the acceleratorpedal end let the car slow down on the engine [in gear] it will not responce when i step on the accelarationpedal, it wil keep iddeling onregular and after 1 min it will pick up again with some smoke for only a instant [if i turn of the ignition and then start again it starts direct and there is power]. With low speed in the city there is no problem at all, only when more power/speed is used the problem occurs

I have changed the dieselfiter and there is no underpressure in the gastank. A LR dealer told me that he want to change the dieselpump [very expensive] but he could not tel me the reason for the problem he also wanted to make a diasnostic of the motormanegmentsystem but i cant believe there is that possibility with a 300 tdi, no where have a spotted the plug for it.

I think it could be the littel pump under the dieselpump [looks like a membreme mechenical driven] but these are in backorder and cost about E 120,-. Anyone has a idee what it could be?

greeting from a desperated belgium disco-lover.

Have you cleaned the fuel sedimenter? Ive heard that a jelly substance can build up in the sedimenter and move around causing temporary blockage to fuel supply.As it floats to the top it cuts fuel of and when it sinks to bottom fuel supply returns.Easy ,cheap thing to check.