Hi

I had my car in for repairs the revs where jumping form 800-1100 rpms while in idle. The garaged did a ultrasonic cleaning of my injections valve's, and everything seemed to work fine until a couple of weeks later. The car broke down and it was towed to another audi dealership, whom first told me it could be some faulty wiring, next it was the engine controller. And last the found the couse of the problem, a short circuit in injection valve number 4. My questions are:

1. Can the short circuiting if the injection valve have been caused by the work the first garage did?
2. Can the short circuiting of the valve be the cause of the engine controller breaking as well?
3. And what are the probabilities that such a thing can occur all by it selv when the car is 3 years old and have about 130.000 km on the clock?

Best regards
Steffen