Ralenti problem of Hiunday Avante 1996

This problem began when the battery disconnects, when it connects my slowdown it went to 2 and before it was 1. What could have passed.
A mechanic told me to distrust the computer?
How can I reset it ??????
Another told me that it was the oxygen sensor ????

I don't know what to believe ????

You can also help me

the manual if someone has it, I would appreciate it very much. ??????

The computer is distrusted, nothing more, it descends the Vateria for about 30 seconds and connect it, then you open the contact 25 seconds and close it 15, repeat this three or four times and in the last one you start it already start, if it does not work it disconnects the battery 3o seconds, and you open and close the contact many times and give it start. On occasions they must give a little filming to normalize, the vateria terminal that you disconnect is always the negative. Good luck and comment.