I have a '92 mk2 8v gti. At the time I bought her there was a fluctuating idle. When I picked her up I set to work on the usual. Firstly was the MOT which was clear (HC/CO well within limits). When the car has reached operating temp, ie 'choke off', the throttle becomes very sharp on/off, and when overrunning to idle becomes very rough - not quite stalling but jerky. If revved on light throttle is fairly clean, on full throttle flatspots then revs all 'pop and bang' and backfires. It also backfires slightly on over-run. If the car is kept under load ie above 1500 and moving, then all is well.
Now I have read all the other topics relating to this, and have changed (myself) the following: Oil/fuel/air filters, oil, plugs, leads and thoroughly carb-cleaned the ISV and throttle bodies. Also I have run a fairly neat mix of STP thru the fuel system. The previous owner had changed the cap and rotor arm, and the coil, although this is a cheap intermotor item. I also observed the plugs I put in were different to those that were in there.
This is an infuriating situation as I bought this car to upgrade from a '91 Jetta TX, which was much smoother and dare I say it more enjoyable to drive. The Golf fault is also intermittent which irks me even more. I have had it Crypton checked and that only showed the old leads were arking. Of note though, any time I have replaced an item, the problem has cleared for a short while, then comes back..........
