VWSpares are inexpensive and i bought my leads, dizzy and rotor arm from them, runs very smooth, its Beru stuff which is a good make.
Check your air filter, make sure its clean, then check the air ducting from there to the throttle body closely for cracks. Also all vacuum pipes, pretty much everywhere you can see check. One tip is to use wd40 while the engine is running around the hoses etc, any cracks will draw it in and change the revs.
As mentioned throttle body clean does wonders.
Then check ignition or buy new stuff as above. NGK plugs are excellent, better than the bosch i had in my opinion, seems to be a smoother burn.
That should sort it.