I climb I alone.

Good friends,
to see if someone would know that it may be due that my vehicle when starting it does it perfectly and remains about 900 rpm, when it limits temperature and the needle comes to mark the first scratch of the scoreboard the car is accelerated alone and climbs to 1500-2000 rpm and it is always, this does it without having stepped on the accelerator at any time because I have purchased it.
If I stop the engine for a moment and start it again at the usual 900 rpm and no longer do it again or if it happens by carrying the car circulating a lot of a march before changing it also lowers me at 900 rpm.
Let's see if someone can guide me and give me some clue, the vehicle is a Daewoo Lanos 1.4 of gasoline.

All the best.

Or you have a small air sucking in some manguerite or the slow march regulatory valve is failing and I do not close the air passing greetings.

It may be temperature sensor too