GOL VIBRATION 1.0

Good morning I have a problem with the engine of my VW Gol 1.0/ 2005 The car presents a vibration in the engine how much it is in low revolution 900 to 1000 rpm the car scanned it and does not present failures which worries me the car is normal to the highest revolutions was made change of straps, synchronization of the alternator particular model usually bother I would like to know if someone has information about this problem and how I can solve it in the best and more effective way thanks and waiting for a prompt response