The symptoms you describe usually occur when an SCV has dirt in it or has some minor damage. The first thing to try is diesel fuel system cleaner. If that fails, pop the SCV (it's on the fuel pump) and give it a clean in petrol. Rinse in clean diesel before reinstallation. If it's still not working, or you can see signs of damage, a replacement would be the next step. In Aus they're over $200 each, so the cleaning is always a first port of call!