No tach movement usually points to the CPS (crank pos sensor). You don't need to get under the hood to replace this or test it. It's kinda behind the right rear wheel, in a crack between the engine and the trans. It's held in by 1 Allen bolt and has a 12" lead and a plug on the end.
Look for the bosch part number because there are less exp options out there than the Porsche part and they are exactly the same.