I own a -85 euro 500 sec with a peculiar problem. When the engine is off, the steering is nice and tight with no slack - i.e. 1mm of movement on the steering wheel is noticeable on the front wheels. As soon as the car is started, however, there is a slack of about 1.5-2 inches of steering wheel movement without the front wheels turning. As you can imagine, this is very uncomfortable while driving highway speeds...the car will suddenly veer one way or the other and I constantly have to correct the line of travel with the steering wheel.

What could be causing this - a worn power steering pump?

Appreciate any help...