Before we begin, it's good that you learn some background information as to what the RPM and TDC sensor do in the car.
The crankshaft reference sensor provide the DME with the timing and position signals of the engine's flywheel for correct functioning and performance.
In Motronic systems, once the crankshaft starts to spin, the DME will pick up the reference signals and will trigger systems like the DME relay, the fuel pump activation, timing and injection.
If this signal is missing, or inadequate, it can generate a non-starting condition and also drivability or performance problems.
This tutorial will teach you how to check these sensors and to try to diagnose them correctly.
If you need to replace the 2 sensors, you can (Buy Them Here - # 0261210002)
***These are basic testing procedures that can be carried out with a Multi-Meter. More extensive testing must be performed with an oscilloscope.***
You will test the RPM Sensor an the DME harness at Pin #8 & Pin #27 and, the TDC Sensor are at Pin #25 & Pin #26.
What you will test with the Multi-Meter is that both the RPM and TDC sensors output an average of about 1,000 Ohms.
Below are some pictures on how to do this...