Volkswagen Polo 2001: Idling problem

I've been told that my 2001 VW Polo has a crankcase ventilation block and requires a breather kit installed to rectify this problem. Could this blockage cause a strange idle, from normal to almost stalling, although the car hasn't actually stalled. I have recently had the throttle body cleaned and an injector service and the car has not got any other drivability issues.