16 valve jtd is a great engine but with 2 weak spots, the timing belt interval is 72k but you would be wise to change it and the waterpump at around 60k max as the pumps have a habit of seizing and taking the belt with them.
Secondly, the inlet manifolds have swirl valves in them, the early design are prown to the bearings wearing and jamming up which will give poor performance as the valves in the second ports will be closed off and leak turbo pressure, and also the control rod coming off which sometimes brings the eml on.
A new manifold is about £170 but its a big job to change as the fuel pump needs to come off, about 6-7 hours. its on the rear of the engine as you look at it and should have a flat bar linking the 4 valves together, if its off and just laying there then you will need a new manifold, the bar isnt available seperatly and once they come off its a sign of worn valves.
Google vectra swirl valves for more info, they use the same engine.