Hi all! My 1.6 Golf C (pierburg 2e2) is generally behaving well, normally starting at 2000rpm, then moving to a more sensible 1000 after a short while of heating up, but sometimes it just goes bananas, ending up with an idle speed of 3500, which I haven't been able to either replicate or make stop once it happens. It seems to happen when the engine is warm though, but haven't been able to find any patterns other than that it may be related to outdoor humidity? (then again, Trondheim is rainy most of the time, so it might just be coincidence ) Any ideas as to what may be causing this, and how to make it stop happening?
Two possibles here I think. Simplest - accelerator cable is sticking somewhere inside it's outer casing, sometimes. More likely, I think; your 3-point unit is not receiving the correct vacuum signal sometimes. This could be caused by a couple of quite different things, one electrical, one vacuum-related. Look at these two images, borrowed with thanks from rubjonny's 2e2 FAQ thread: The thermotime valve (TTV), number 11, either allows or blocks atmospheric pressure air into the three vac hoses coloured pink. If it allows the air through then the vacuum signal to the 3-point unit (2) is 'spoiled', and the actuator of this will be at full extension, pushing the throttle open widely enough via screw 3 to cause revs of around 3000 on a fully warmed up engine. This 'no vac' situation could also be caused by a leak in any of the pink vacpipes or connections, unfortunately these ones are a bit hard to inspect well with the carb in place. I would suggest you do check them though. See if you can provoke the high-revving by waggling theese hoses around while the car is idling normally (when fully warm). The TTV is an electrically heated air valve, which is open when cold (<15C approx.) and closed when warmer than that. Normally it is only open for a few seconds during the first phase of cold start, if the under-bonnet temperature is low enough. The colder the ambient temperature, the longer it stays open, effectively immitating a driver pushing the accelerator pedal, via its influence on the 3-point unit. The electrical power is provided by the two-way electrical connection, which should have 12V between its contacts whenever the ignition is on. Check that your TTV is getting this power feed. If it is not, the TTV will open and close according to how much heat it is being directly subjected to by the surrounding air in the engine bay. Next time you get this behaviour, look at the actuator/plunger/piston of the 3-point unit while the car is revving itself, if you can stop safely to open the bonnet and look. If you find this plunger fully extended, to about 14 - 15mm, and the screw '3' touching the end of it, then I think you can rule out the accelerator cable being the problem.
Between exams and work before Christmas, I never got around to looking at the problem until today, and it turns out the electrical wire to the TTV had broken and the break was hiding behind the vacuum bottle. All is now well (hopefully!), and the car is idling like a champ! Got a strange rattle somewhere, but that's for another forum Thanks a lot! You're a great resource for the 2e2 problems we all face
