All right, seems like you have done quite a bit of work to fix this concern. Let's see, new rings, new cap, rotor and wires, swapped injectors from cylinder one to cylinder three, and the plug will fire when removed from the cylinder. I assume that the plugs have been moved around. What type of plugs are you using? Platinums and brands like Autolite generally do not do well in this engine. When you had the head off to re-ring the pistons were there any cracks present (common between the valves but fully acceptable) or excessive carbon build up on the backs of the valves? Is there enough air entering the combustion chamber (possible bad lifter?) When you performed the compression test did the reading for cylinder number three rise as quickly as the other three cylinders? The timing is most likely good. Any excessive cam wear? A lot of questions here, just trying to think out loud. I have an 86 4000 with over 300k and no problems with the fuel injection yet. Hope this helps to think outside the box. If you have any more info please send it. Max
Makes sense to me as all of the other possibilites have been ruled out. The inside of the idle control is worth cleaning regardless of how it looks. The actuator will move when it is rotated side to side quickly.
Don't feel dumb about this, I can't tell you how many times I have overthought a problem when the solution was right there is front of me, someone usually walks by and points outg the problem, duh.
I hope that you are able to find a new distributor. Try and find out what other Audis the part number cross references to. It may be easier to find one of an 5000 for example. Good luck with your search and congrats for finding the cause of the concern. Max
Hey XXXXXXXXXX,
Great to hear that you have the vehicle running well. Thank you for getting back to me with the good news. As for why the idle drops and the engine dies with the oil cap off I am not 100 percent certain. I did check this on my vehicle and the engine stays running with no real drop in the idle. But I have a slightly different breather system. The crackcase is vented through the cylinder head on my engine and not the block. I don't think that you have a bad idle air control (IAC) valve. When the IAC fails the engine will either not hold and idle or will be difficult to start. On newer VWs the idle will drop if the oil cap is removed as you are creating a large vacuum leak, probably what is happening to your engine. Unlike the newer models the older ones did not adapt to large changes in the air/fuel mixture quite as quickly. As long as the engine is running well and you do not have excessive oil consumption I would not worry about it. These engines should not be using very much oil, if any. Sounds like your son may have a decent car for not a ton of money. Congrats. Max
VW Shop Foreman
VW certified lead technician, ASE certified Master Technician, 10 years experience