robotshop rover

Hi all, Ive been messing about with arduino now for a while and have decided to try and use one in a project. The project I decided apon was a robot... I picked up a roboshop rover and put it all together and used an L293D motor controler and sharp ir sensor, all worked fine.... it was avoiding things as told and I was happy, but then I decided to add a couple of servos and extend my scaning range... thats when things started going wrong! the code for the servos tells them to scan right then left anf that all works fine but then I included the code for avoidance and the servos made one scan and jammed over on one side as soon as i started driving the motors! I hope i have explained this well enough and if anyone has done, seen or heard of anything simular could they point me in the right direction please....

If its not a sketch logic error perhaps a bit of decoupling is called for?