I have a 92 GTI w/208,000 miles. The car runs like a champ, no problems. Previous owner said he advanced the timing a little for better performance. I decided to have a mechanic adjust the idle back to stock specs because it was running a little rough prior. What happens is when i push the clutch in and the idle drops all the way, it will almost kill the engine before it immediately comes back up to the stock idle speed and stay there. Does it 90% of the time. There is also a slight idle surge every 4-5 seconds of around 50rpms, not a big deal. Granted the engine has 208,000 miles without a rebuild, but do you guys have any ideas.
With an advanced timing, the idle screw needs to be closed to maintain proper idle. Now that the ignition timing is retarded back to spec, the idle will be lower. The ISV is able to compensate, but you will see the dipping idle before it's able to compensate. Turn the screw out a little at a time, rip the throttle, and watch how it comes back to idle.
The 92 has Digifant with knock control. What do you mean by rough running beforehand? Is it smoother now? Digifant has a special method of setting the base timing. Are you sure it was done correctly?
It had a rougher idle is what i meant to say. I adjusted the idle screw out a little, seems to be better now. I plan on replacing the pcv valve and grommet, and clean the hell out of the louvered vent under the valve cover. It was gummed up bad last time i noticed.