Over the years it has become apparent by reading the problem pages of VW Motoring and Volkswagen Audi Car magazines that there are a lot of GTI's around that are suffering from idling problems. I also suffered from idling problems on the two GTI's that I have had. Both of them had the PB Digifant engine, one of them an '88 model and the other one a later '90 model.
After a period of time the idling would become erratic on cold start, with a tendency to not idle at all on occasions, bloody annoying if you have to keep stopping and starting in traffic. The damper weather appeared to affect the idling. Some people have suggested that it is "impossible to get a GTI with that injection system to idle properly". I have only one answer to that and it begins with 'B' and ends in 'ollocks'!
One of the solutions is to remove the idle stabilisation unit out of the car and clean it up and then dry it. I have tried this with no effect. My local dealer then tried a different approach, by taking the idle speed screw out and then cleaning it up. If you take the screw out of the housing you will be surprised by the amount of black carbon gunge that has stuck to it. Clean the screw up and also the hole from which it comes. If you want to be through take the rubber inlet housing off from the inlet manifold by removing the metal clamp by slackening the screw. This will enable access to be gained to the throttle body and the idle tapping. A clean out of this area would not go amiss.
Replace the screw and the inlet housing, and adjust the idle speed. This should now result in an engine that idles fine. When you notice the idling playing around again, then the screw should be cleaned up, and a gap of about 6 months in between cleans will be found.
You might think that this is all well and good by I don't have a Digifant GTI. All the above information is applicable to the K-Jetronic injection system as well. This problem existed on the F%*d Escort XR3i Turbo Nutter dickhead roller skate. So go on K-Jet boys, give it a whirl, it might work.
To setup the idling the official way (from Stu Evans):
1. Start the engine. When at normal operating temp, disconnect the BLUE plug from water pipe on front of cylinder head. Rev engine PAST 3000RPM 3 TIMES. (This resets the ECU).
2. Alter the idle using the screw in the throttle body. Set it to 850/900 RPM. When happy, re-connect the blue plug.
The idling should now be OK. If it is not, then you may have a fault on the blue sender
Top Tip: To get an accurate rev count, use the MFA in one of the 'secret modes'. See the other articles