This problem gets asked about 'quite a bit' on the forums - It applies to the mk2 Golf/Jetta 16v with KR engine.
"My mk2 16v cuts out at junctions and idles terribly, I'm at my wit's end"
Ok, there are somethings you can check yourself at home.
If the ISV is working ,turn ignition on pos2 valve should *buzz*,
Make sure it isn't cogged up with oil deposits-either replace it or flush out with carb cleaner.. remove the brass air bleed screw and clean it also. If all that fails .........
Try cleaning out the inlet tracts of oil and the airflow flap. If the engine isn't hunting when cold or hot, the CO is correct. 16Vs run best at 2.0 % CO.
To achieve 2.0%, disconnect the famous "red lead" spade connector behind the coil (see fig:1 below) (after the engine is at temp), pull off the breather hose and block the airbox hole. Start the engine and the revs should plummet, if they don't, the idle valve is shagged and you're idling off the bypass screw alone. Now, with the engine running, turn the idle screw (fig: 3) up until you get 950rpm +-50.
If the idle wanders or is lumpy (engine visibly rocking), insert your LONG 3mm allen key into the CO screw (fig :2) and turn it anti clock to weaken. Just prior to the engine cutting out, turn the key clockwise in 1/8th turn increments until the idle smooths out. Eventually, the engine should settle to a nice, steady idle. This will be 2.0% or very close to.
Switch off and reconnect everything.
Take it out for a run and when you dip the clutch, the tacho needle should gently fall to 1000rpm, not plummet. If after all that it's still missing and rough, investigate air leaks around the inlet manifold and the various vacumn hoses.
If you ever need to find the controller for the ISV it's the black box with 'VDO' marked on it that's clipped to the back of the ashtray or (if someones been fiddling), shoved behind the dash in a random fashion!
If you're really unlucky and the above instructions don't sort out your particular idling issue,check that the three senders on the end of the head, under the distributor are working, 2 of these control the ISV and the other is the temperature gauge sender - the senders are all the same so as long as your temperature gauge works, you can swap the wires to make sure all 3 senders actually make the temp gauge register, obviously if one doesn't work, there's your faulty sensor.
WARNING -The sensors are about £20 from VAG so be careful whilst tightening them, they are tapered thread which means in simple terms that you don't wind them in all the way!
Thanks to Kevin Hayward for the original version of this posted on the Club GTI mailing list, many moons ago and GVK who's website I pinched this particular version of the info from
