It is urgent with derby starting or polo classic 05

Greetings to all. I'm from Mexico.
3 weeks ago, buy a Derby or Pole Classic 2005 used in an agency, and everything was fine the first week. In the second week I realized that it was accelerated between 1000 and 2000 rpm and the only way that it "fades" was to go to the dead point and give it an acceleration. When it was stopped (at a high, for example) the slowdown stayed at 1200 rpm instead of the 750-800 rpm normal I "faded" solo after a few seconds, or still gave him the acceleration.
They would take him to compose the problem (they gave me 30 days of "guarantee" in the agency) and they gave it to me to the next day. Everything seemed to have returned to normal. As I was in a hurry they didn't tell me what they did to me.
I left the city and I had the car stopped 5 days and today that I needed it, it did not start.
It seemed to have little gasoline and put 6 liters and nothing. The battery is fine because I can light the lights, the radio, the air conditioning and go very well. Not to mention the oil, your levels are well. At first he went and did not start the car, after attempts to turn it on using the technique of "pumping some gasoline with the accelerator" the engine began to start but only for a second or two and then go out, it does not continue walking. After a couple of minutes he did not pump him so as not to "drown him" and nothing. So he continued for a while until more or less the engine remained on as 3 seconds which is not progress. Needless to say, until today I had not given the start.
I understand that engines need 4 main things that are: gasoline, oil, electricity and air. According to what from the beginning it has been bad is the entrance of air and it seems to me that when repaired they made a chambonada to the vàlvula IAC or something related and they left me worse. What do you think?

You took out some spark plug to see their status, that is, whether they are wet or not? Check them and see