I have a Frontera 1996,2.8 tdi,128k,The problem is when cruising at 60 mph/2500 rpm,the engine gets lumpy and doesnt run to smoothly,but if I put foot down just a tad and run up to 70 mph it pulls lovely and smooth,but as it drops back to 60mph it starts again getting lumpy,It only seems to happen at 60mph/2500 rpm though.I tried replacing all filters and oil but no differance....Any ideas..Thanks
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