First of all I don't think it'll be the injectors, they rarely go wrong. It is worth putting redex (my personal fav) through the engine system and see if that clears anything up, however don't expect miracles as injector cleaning is done on a bench and they are cleaned using ultrasonic equipment, cost is around £80.
I'd try the free/cheap stuff first, which also seems the most common.
Clean the throttle body with carb cleaner. This is the easiest and one of the most common issues. Only 4 bolts holding the throttle body on, and a few pipes. Remove all them and clean the throttle body thoroughly with a toothbrush, some tissue/towel and carb cleaner.
Other common problem is the ECU relay. For these go directly to VW as they are cheap enough (around £15 last time I bought one).
Also check the spark plugs, rotor arm, and distributor cap are in good condition. They may be causing a slight misfire.
Does it misfire/judder when you put your foot down? If so it could be the spark plugs and cap and rotor as I said above, but also the ignition coil as I experienced a few weeks ago.
Have a look here
http://www.golfgtiforum.co.uk/index.php?board=8.0Here
http://www.golfgtiforum.co.uk/index.php?board=57.0and finally here
http://www.golfgtiforum.co.uk/index.php?topic=101400.0