Audi A4 Stops every few seconds.

I am not very technical with my description so please bare with me. I will try to answer all the questions.
Model: 1998 Audi A4 1.8T
Front Wheel Drive.

Few days ago i serviced all brakes pad change, and replaced front driver side rotor which was gonne bad. This was done with a private mechanic who does one car at a time for such maintenance. While he was leaking brakes, the engine was working fine. As you know during the leak you need to turn on car and hit constant brake. At this time my engine was perfectly fine. Car was on for the 10 minutes of duration without any problems. After then, he attached back tires and went for test drive. No problems so far.

Then he decided to mess around with ABS and Brake light that is displayed on my dashboard. ( This lights are displayed due to cencor issues, as Per AUDI dealership the Cencors needs to be replaced. There is nothing wrong with ABS. Brakes are fixed. )

So he decided to reset my car, which will clear off the lights, He unplugged one of battery cord ( The right one, i dont know which one, but i did confirmed with a friend over the phone that he pulled of the right one)... Left on for few minutes.. Hooked it back up..

So i was about to leave.. Started my car.. As i start my car, the firesup fine.. but in next few seconds, it starts to shutdown... when i push on pedal to keep it alive it wont do anything.. it will shutdown every few seconds..

I turned my car on, quickly put on reverse to see what happens, It shuts down in few seconds.. I am very frustrated with this problem and have no means of transportation past few days.. I want to figure out problem before i could take it down to any place to fix it.. Apparently people here are just looting customers who are not so techinical..

Please help!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Sounds like something went wrong with your ECU.
Is the garage where you fixed your car authorized by Audi?
You will have to take your car to an authorized audi garage, where the can read your ECU for faults properly