Hi, I'm done a project of a car with arduino and xbee with 4 motors and a driver l293d and for power the driver I use a battery holder with 4 batteries of 1.5 v AA but when doing the car the engines turn very slow and can not move the vehicle and already check the voltage of the batteries and it is correct I hope your help and opinion of what is the problem
You could try more voltage, say 6 x AA batteries and make sure they are alkaline AAs not cheap ones. L293D is very inefficient and will commonly drop 2-3V so your motors are probably only getting around 3V.
Another possibility is that your (unspecified) motors are trying to draw more than the 600mA that an L293D can supply. In that case you'll need a different motor driver.
Steve