Okay.
An hour ago (exactly at 10:37 PM on April 1st, 2004), the brand new ESP in my 1Z came to life. It took a long time and some troubleshooting before we realized that the central screw on the back of the pump was not tightened (already from Bosch!) and that the pump was therefore not pumping. Now, the jerking

is finally gone. It cost 1050 EUR plus 160 EUR for the timing belt, tensioner pulley, idler pulley, and ribbed belt, but in the long run, it's worth it.
Unfortunately, the old pump has to be returned to the Bosch service center. Otherwise, it will cost me the €200 deposit

.
So, anyone who is interested in a pump that might be slightly noisy but otherwise works perfectly and is willing to pay 200 EUR for it, is welcome to contact us until Monday

.
Smooth greetings.
Hermann.