Idle Stabilizer Control Unit - van won't stay running without it

[jb20thae]

I was trying to check the timing on the van today (2.1L), however after unplugging the box behind the passenger side tail light the van wouldn't stay running unless I kept on the gas pedal. It was my understanding that this "ISCU/IS" (what IS the proper name for this box?) should be unplugged for proper timing. Am I doing something wrong or is the timing so far off that it needs the ISCU to stay running?

[jlrftype7]

I believe you’re getting your later System confused with the older Digijet system with the Idle Stabilization Unit that has two plugs which get plugged together to bypass the unit and allow timing to be set correctly.
I don’t think you disconnect the Idle ECU that controls the Idle Control Valve on your later Digifant system for Timing adjustment
Others can confirm this who have more info with the Digifant system.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[Howesight]

Hi JB:

You don`t need to use the Bentley procedure to set the spark timing on the 2.1 Digifant engine. You simply rev the engine to a set rpm and turn the distributor to obtain the specified timing. I don`t recall that specification off the top of my head, but here is a link to a post by TenCentLife who first explained this clearly:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

Regarding the inability to keep the engine running with the idle speed control system disconnected, if all is set up to specification, then the hot idle speed, without the Idle Control System operating, should be around 840 rpm. The ISC then adjusts this.

If your disconnected idle speed is lower, then you can adjust it using the large screw in the Air Flow Meter. However, you should first check for vacuum leaks since they can affect idle speed, and idle quality, a lot. I saw some of your photos which seem to show, among other things, a possible vacuum leak at your breather hose. The accordion hose between the throttle body and the AFM will often develop cracks that are only visible if you remove the hose and bend it while under strong light. There are several other possible sources of vacuum leaks.

The digifant system injects a set fuel quantity at idle speed and the air introduced through vacuum leaks is not measured by the AFM. This can result in a lean condition that produces a rough idle. Once the coolant temperature hits its threshold, the Lambda system begins to correct any lean idle condition. This can explain why in certain conditions, the engine runs roughly, but moments later can run well again.

Here is a link to the updated Digifant Pro-Training Manual updated by Kamz:

http://oldbluesblog.com/files/DigifantProTrainingManual_SingleSided.pdf
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'86 Syncro Westy SVX

[jb20thae]

Ah, right, Thank you both. I'm confusing the two idle control mechanisms. The box behind the taillight is Digifant and the one by the coil is for Digijet?

The van not staying running with the idle unit unplugged is likely due to vacuum leak or afm mix needing adjusting? The afm is a 10yr old rebuild with open access to the adjustment screw, but it's new to me and I haven't messed with it.

The pics you may have seen (I'm guessing of the throttle body?) are from a second vanagon we have currently. This particular post is for a different van whose s-boot I removed and inspected pretty thoroughly as part of the work I was doing today.

[jlrftype7]

[hardway]

There is a large screw on the throttle body. It adjusts the air volume that bypasses the closed throttle blade. You can increase the base idle speed there. Setting the CO by turning the bypass screw in the air flow meter should be the very last step in adjusting things. The sample port in the J-pipe before the cat is how CO was measured and adjusted at the factory. I use a voltmeter and measure the output of the lambda probe (oxygen sensor) with the probe unplugged.

[Howesight]

Hardway is absolutely right in his post above. Excuse my brain fart.

The large screw in the photo below (above the red circle) depicts the screw uses to adjust idle speed:

The screw in the AFM adjusts base CO and should be left alone until all other reasons for incorrect CO are eliminated.
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'86 Syncro Westy SVX

[jb20thae]

To clarify for my understanding, when properly tuned, from an ignition off state the van should or should not be able to start and idle with the digifant idle control unit unplugged?

[jb20thae]

To clarify for my understanding, when properly tuned, from an ignition off state the van should or should not be able to start and idle with the digifant idle control unit unplugged?