Problems after engine wash

Hey, guys.

I am a freshly baked V8 owner (3.6l, 1990, automatic machine). The car ran with checkbook and so far impeccable.

This morning, however, I had to have the engine washed (vehicle inspection at the traffic office). This happened in a VAG garage, which makes Audi/VW/Porsche. Since then, the V8 has problems, which have not gone away even by some driving (always about 300km at a time):

* At any time, the engine is suspended; it seems that the fuel shutdown is active, although power is needed. On the moment consumption, the display goes to 0.0 when this happens (visible on the highway if the failures last more than 30 meters). This is a quarter to half a second, and then the engine starts up again fully (with the corresponding jerk on the vehicle). This seems to have become less frequent with driving, but continues to occur. Also often happens in the low speed range (feeling like starting a rider in the first driving hour at *g*).

* After it has become cold, the engine goes off immediately after the start (after a second). The same happens when holding, e.g. at a crossroads or on a pedestrian lane (very unpleasant...). If I give gas right away, it works OK - as long as I stay on the gas. If I go off the gas to take a gang, he'll go out in a minute. However, if I stay on the gas lightly to insert the whole, there is no problem. With warm engine, the idle speed fluctuates up and down, but without running out.

* It no longer switches correctly, but usually stays on the 3 slopes. Switching down does not happen if you go from hand to hand to 2 or 1, but only if you slow down accordingly. In the 4 he no longer switches, and turns up accordingly on the highway. The display in the cockpit is correct.

* Kickdown is no longer running.

Well. I went back to the garage in the afternoon. They've read out the bugstore and found out the following:
* Kickstart sensor is constantly on mass
* Consumable sensor is sporadic on phase
* Consumable sensor is sporadic on mass
(* Another short-circuit error that I no longer know by heart)

Apparently, water's in somewhere and doesn't want to evaporate. Where? The mechanics were looking for an hour and found nothing, and now I have my next appointment there on Monday. However, a hint where I could look for moisture/water would be helpful.

Thank you!

Arsène