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Blanking off the EGR on an old diesel is a good start, but it could be closing the stable door after the horse has bolted. That's because the EGR doesn't just recirculate exhaust gas, it recirculates soot and unburned diesel as well. These two mix together and coat the inside of the entire induction system with a thick, sticky goo. This builds up and can entirely block the inside of the inlet manifold and inlet ports as well as the EGR valve itself. My last car was a diesel and it had a 5mm layer of this gunk all over the inside of the manifold. Cleaning this and the EGR valve gained me 15 bhp and a much smoother, more responsive engine. A thicker layer would have robbed me of more power. I've seen photos of EGR's that were almost entirely full of this stuff, so the manifold would be the same. I strongly suggest you get the inlet manifold off and clean inside it and the inlet ports as well. Just make sure no muck gets down into the engine. You will probably need new manifold gaskets to ensure a good seal. Use Carb cleaner and wear rubber gloves, no kidding. Check the air filter element is not clogged. Check all the hoses between the turbo and the inlet manifold in case any are leaking and losing your turbo boost pressure. Check that the outside of the intercooler is not blocked by dirt and debris. If it is not cooling the inlet air, it will be robbing you of power. Get some fuel system cleaner like PowerEnhancer. This cleans the injectors, fuel pump, and combustion chambers and costs about £20 when on offer. Make sure you follow the instructions fully. Birmingham Audi are doing an offer at the moment for something similar for £15. Or you could try TerraClean (instead of PowerEnhancer), which is like a power washer that cleans inside the engine's combustion chambers. Expensive at about £70 or more a go. Start using a good fuel like Shell VPower that continues cleaning the fuel system after the PowerEnhancer has done its job. Use it exclusively for the first month then one fill-up in every four or five to keep the muck from building up. Take off the catalytic converter, turn it upside down and thump it fairy gently to loosen and remove the built-up soot inside it, then put it back on. This reduces the resistance to the exhaust gas flow. There might be blow-by around the piston rings, losing pressure and therefore losing power. There might be a leak from the cylinder head gasket, also losing pressure and therefore losing power. Have the fuel pump checked to see if it is giving enough pressure to get the right amount of fuel through the injectors. Have the injectors checked to ensure they are working properly.