how can i fix my peugeot 406 2.1 diesel?

my car is hard to start. Have had new glow plugs fitted and the injectors serviced. Still hard to start, but when started idles good. When trying to rev up the engine revs up a little and then cuts out. I pulled the wiring off the trottle control unit, the one with the trottle cable connected to and the engine seems to idle better.