High idle

[hardway]

Have you tried pushing the throttle shut by hand when the high idle happens? Closing the throttle air bypass screw all of the way? Checked for continuity at the closed throttle position switch, especially when the problem happens? AC request off? You can unplug the AC input at the compressor. You can unplug the power steering load switch at the pump, but don't short the wire to ground by accident. Check for vacuum leaks?

If so the next step is to measure the control current to the idle air valve. Put an ammeter in series with the valve and wiring. Or you can borrow a known good idle control unit from a healthy van. I had one once that still had an intermittent high idle. A different engine control unit fixed it. It apparently had an intermittent profound problem with fuel or timing control. I never did figure out exactly what caused it. But a different ECU fixed it.

The key is to be able to perform all experiments over and over with repeatable results. Divide the system into sub components and test between and during failure episodes. But it sure sounds like the throttle isn't closing reliably.

[borninabus]

if your throttle body is original, it is worn out, guaranteed. replace it!
if that doesn't work, unplug the ISV and set the idle when warm using the screw: old school style.
leave it unplugged and if everything else is good, this will work for the summertime.

when winter rolls around and it wont idle on cold start, you will have to get down to the nuts and bolts of the FI system from rebuilding the injectors to cleaning grounds, testing fuel pressure and the ISV AND ICM AND more than likely replace them both. or you can just give it some gas for about 30 seconds: old school style.

the digifant idle system is something that you will have to research and figure out what is the best way for you to "fix" the "problem"
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[syncro2x]

I had that problem twice on 2.1 vanagons. Both times it was idle stabilizer control unit. Stayed at like 2800 rpm and would not come down. Have had to get a new throttle body on a 3rd vanagon, it idled like 1500 rpm, let clutch out a bit and it drop down.

[supdave66]

[quote="hardway"]Have you tried pushing the throttle shut by hand when the high idle happens? Closing the throttle air bypass screw all of the way? Checked for continuity at the closed throttle position switch, especially when the problem happens? AC request off? You can unplug the AC input at the compressor. You can unplug the power steering load switch at the pump, but don't short the wire to ground by accident.

Throttle is closed. Checked the throttle body switch with a meter. It’s closed at idle and open when you move the throttle. Removed wire from air conditioning compressor and the two wires from the power steering pump. Unfortunately none of that worked. It idle great when I unplug either the idle control valve or the idle control modular. Can it still be a vacuum leak if it idles fine with that stuff disconnected?

[supdave66]

[supdave66]

[quote="borninabus"]if your throttle body is original, it is worn out, guaranteed. replace it!
if that doesn't work, unplug the ISV and set the idle when warm using the screw: old school style.
leave it unplugged and if everything else is good, this will work for the summertime.

Interesting, I did not know I could run it with the idle control valve unplugged.
Thing is driving me crazy. thanks for the help

[hardway]

Successful diagnosis is always "divide and conquer". A high idle speed can be due to too much fuel, over advanced ignition timing or too much air entering the system. If you want to determine experimentally if too much air is entering the engine through the idle air control valve or if the problem lies elsewhere then pinch off the air supply hose to the air valve. If you close that hose and the idle is too high then the problem is elsewhere. If you pinch the air supply hose to the air valve fully shut and close the idle air bypass screw at the throttle you should be able to stall the engine or at least get the idle really low.

If you test something and it passes the test it only means that it passed the test at the time that you tested it. It does not mean that it would pass the same test at other times. Something else to consider is the act of observing frequently interferes with the observed. The Heisenberg uncertainty principle. Originally applied at the sub-atomic level it has validity at the macro level also. So in formulating your testing procedure you to be mindful to interfere as little as possible. With this in mind do you know for a fact that the closed throttle switch is working during a malfunction episode?

If your problem is fairly consistent then it should be fairly easy to prove the relevant facts experimentally. Intermittent problems not so much.

Good luck!

[supdave66]

[quote="hardway"]Successful diagnosis is always "divide and conquer". A high idle speed can be due to too much fuel, over advanced ignition timing or too much air entering the system. If you want to determine experimentally if too much air is entering the engine through the idle air control valve or if the problem lies elsewhere then pinch off the air supply hose to the air valve. If you close that hose and the idle is too high then the problem is elsewhere. If you pinch the air supply hose to the air valve fully shut and close the idle air bypass screw at the throttle you should be able to stall the engine or at least get the idle really low.

Ok, I clamped of the intake side of the idle valve, after it was warmed up. It idles but very low, somewhere about 500 to 550. I used one of screw type clamps from harbor freight. Started to unscrew it slowly and I can hear the idle raising. The more open it was the higher the idle, all open it goes to 2300

[hardway]

Progress. You have proven that the high idle speed is caused by air passing through the idle air control valve. The VDO idle control system is piggybacked onto the Digifant system. BMW did that in the eighties on the M10 engines, those had problems too. I used to take a copper pipe cap and drill an orifice in it to limit the air volume going through the air valve on the M10 engines. I put the pipe cap in one of the air hoses. That setup was even more problematic than the 2.1 wasserboxer.

The pattern failure is the idle control unit. When everything was available I used to throw a control unit and valve at the vehicle. Of course the more frequent and persistent pattern failure is the throttle switch and body.

It would not hurt to inspect the wiring. I would check the wiring, power, ground and inputs at the control unit gang plug. I always check the control current going to the valve because that is what the repair manual said to do. I made that test harness in the eighties.

I used to replace the valve with the control unit because a short circuit in the valve would kill the control unit. But experience has shown that the two wire air valves are electrically robust. As long as all of the wiring pins out OK you are safe to just change the control unit.

Overcoming challenges make you stronger. Good luck!

[supdave66]

Update!!
Problem fixed!
I borrowed a bunch of parts from a working vanagon and swapped things out one at a time. I thought for sure it was going to be the idle Control modular. Good thing I am not a betting man. Lol. Ended up being the idle control valve. I tried everything and I still could not get the old one to work correctly. It would buzz and act like it was working properly with the ignition in the on position, but would make the Vanagon idle at 2500.
Thank you for all the help.

[borninabus]

sometimes you can give them a good clean-out with carb cleaner and adjust the little allen screw inside the plug end to bring them back to life.

glad you found it!
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[supdave66]

[Keeponbussin77]

I'm glad you have found your answer! I was hoping you folks could help me suss out mine as well.
I have an 86 Vanagon with the 2.1. Bought it about six months ago and have had no issues until about a month ago when cruising down the road. All of a sudden the idle would not drop in the engine. Got it home and checked out a few things and found my Throttlebody and TPS was in pretty rough shape; So I replaced it. Now this solved my non-consistent idle problem, but it now consistently idles at 2300 RPM. I have found that if I unplug the ICV the idle drops to normal; so I did the vibration test and cleaned it; no difference. So I replaced it as well. Still no difference. I've checked for vacuum leaks and have not found any. I'm getting fairly stumped at this point, do you guys have any idea what could be causing it?