Have very low power on my 98. It has a cone air filter, tbh not delved into it too much, as didnt really realise how bad it was till other day. Have no egr valve, no maf sensor. Has a silly cone air filter on. The intercooler to inlet manifold hose is very soft. There is also an oily residue on the turbo to intercooler metal pipe. There is a non return fitted in the fuel line just before the FIP, It does need a bit of oil adding as just on the minimum. There is also an oily deposit around number 1 injector. I think i will be changing the leak off pipes, as all seem towards the end of their life, but not appear to be leaking diesel. Ecomomy is also only around 17mpg, but I do mainly a 4 mile eack way commute to work.
Only had the car a little over 6 weeks. My 200 and 300 tdi discos go a lot better, and the 300 has not been fiddled with and running big lift and tyres. Pulling out of junctions has definatly got more "challenging".
I have read various threads on here and BMW forums about various power issues, and tuning procedures. But info on amything relating to the m51 lump is a blit like rocking horse ****.