CAR giving Missing ( Sort of Backfiring)

We had purchased Tata Indica Vista from PAWA motors in Dec 2008.

From the very beginning the car gave the following problems:
1. Car Fan vibrating when ac turned on
2. The car would start giving missing and accelerator won't work, but this was not on a regular basis, which further made the car very unreliable. We would never be sure if the car will start or not.
3. Brakes freeze sometime while ac is on

We had many times complained to the agency and they did their best to resolve the problems. But they were not able to rectify the Missing Pulse Issue, though other starting problem were temporarily resolved. This has been going on for last 1 year.

We have been told by the agency that the car piece is defective and has to be changed. But even after changing it the car did not stop giving Missing and that is why the above problems are not being permanently solved.

We have already wasted a lot of our time, energy and money for this car. This car is bringing a real bad name to Tata.