You will most likely begin diagnosing this troubling issue by starting with the trigger points. In the bottom half of the distributor you will notice a set of breaker points, these are responsible for pulsing the injectors at the correct time. Begin by removing and checking to see if they are coated with oil. If they are, clean them with a dehydrating solvent (brake-clean..etc.) reinstall them and monitor the engine performance. You may also want to monitor the input/output voltage to these points while in operation. This is one of the oversights when diagnosing a D-Jetronic performance problem.