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More idle control issues.
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zoti
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PostPosted: Sat Aug 28, 2021 7:39 pm    Post subject: More idle control issues. Reply with quote

As part of the development of the idle control unit I am testing the ones I have.

1988 2.1L Digifant. I have 2 idle control units. One is a rebuilt by module master. The other is just a B model.

Testing per the Digifant trouble shooting manual for 430MA +-
20MA at idle and I only get about 26MA reading. That's on both the rebuilt unit and other unit.

Image may have been reduced in size. Click image to view fullscreen.


The idle control valve does open a bit. If I disconnect it, the idle drops a little. I can also connect a second valve I have and see it open

Running both units off a 12v power supply on the bench gives me the same results. I power them by connecting 12v to terminals 15 and 31. See diagram below.

Image may have been reduced in size. Click image to view fullscreen.


The ICU also gets power on terminal 50 and I am trying to figure out why exactly. So far we think it's a signal to the ICU that the starter is engaged.

I should note that other than the slight rise in RPM that is always there, the ICU does not seem to raise idle when the power steering is engaged or the power steering terminals are jumped together.

Looking for insights from more experienced people.

Tomorrow I am planing to test each and every wire. I find it hard to believe that both and especially the rebuilt idle control units I have are defective.
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DanHoug
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PostPosted: Sat Aug 28, 2021 7:46 pm    Post subject: Re: More idle control issues. Reply with quote

the throttle body plate rest point is a crucial measurement, set via vacuum specs on the TB canister valve port. if that is too open, the ICU will not have the range of adjustment at its disposal.
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60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

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Vanagon Nut
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PostPosted: Sat Aug 28, 2021 7:52 pm    Post subject: Re: More idle control issues. Reply with quote

AFAIK, the idle control system (i.e. valve) compensates for added loads. IOW, instead of raising the idle when PS and/or AC loads are introduced it tries to maintain the idle speed by allowing more air into the intake.

50 positive would be present when starter is engaged. I don't think you should see 12 volts positive at that 50 pin/wire at any other time.

Neil.
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zoti
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PostPosted: Sat Aug 28, 2021 7:57 pm    Post subject: Re: More idle control issues. Reply with quote

Vanagon Nut wrote:
AFAIK, the idle control system (i.e. valve) compensates for added loads. IOW, instead of raising the idle when PS and/or AC loads are introduced it tries to maintain the idle speed by allowing more air into the intake.

50 positive would be present when starter is engaged. I don't think you should see 12 volts positive at that 50 pin/wire at any other time.

Neil.


I agree about terminal 50.

I used an oscilloscope to try and read the pulse of the ICU. (It works great when reading the hall sensor). All I get is a dirty signs. Nothing stable.
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zoti
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PostPosted: Sat Aug 28, 2021 8:00 pm    Post subject: Re: More idle control issues. Reply with quote

DanHoug wrote:
the throttle body plate rest point is a crucial measurement, set via vacuum specs on the TB canister valve port. if that is too open, the ICU will not have the range of adjustment at its disposal.


That would be the throttle position sensor input which is adjusted correctly.
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zoti
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PostPosted: Sun Aug 29, 2021 9:52 am    Post subject: Re: More idle control issues. Reply with quote

I have basically tested everything I can on this and the only conclusion I have is the both idle control units are defective. Even the one that was refurbished.

I have power to the ICU. I have hall sensor signal. I have temp signal and the resistance is exactly where it should be (I get 230Ohm at full warm engine).

Yet I can't get 430ma at the idle control unit or pull a signal off it with the oscilloscope but the valve is slightly opening and raising the idle.

It will not raise idle when I bridge the power steering switch. Not sure about AC because my AC was removed by the previous owner so I just have the wire that went to the compressor. I don't know if the ICU receives a signal from that wire or ground when you turn the AC on.
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Vanagon Nut
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PostPosted: Sun Aug 29, 2021 10:56 am    Post subject: Re: More idle control issues. Reply with quote

ziti wrote:
Yet I can't get 430ma at the idle control unit or pull a signal off it with the oscilloscope but the valve is slightly opening and raising the idle.

It will not raise idle when I bridge the power steering switch. Not sure about AC because my AC was removed by the previous owner so I just have the wire that went to the compressor. I don't know if the ICU receives a signal from that wire or ground when you turn the AC on.


Double check this but '86-'89 AC wiring diagrams show a positive wire to ICU; as AC compressor clutch relay closes, positive gets connected to ICU. (to pin 2K, I think).

I guess if van is stationary, one would expect to hear/see the idle increase if the PS switch wires were connected eh?

Somewhere in this forum there's a pic I posted of a Mercedes idle valve showing its' valve positions at various duty cycles. IIRC it's similar to the Vanagon idle valve.

Neil.
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RawUmber
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PostPosted: Sun Aug 29, 2021 11:30 am    Post subject: Re: More idle control issues. Reply with quote

26mA is obviously out of spec, and might not be able to operate the ISV at that point. Is the amp meter hooked up correctly? It should be in series with the load (ie, ISV). Ex: between the ISCU ST2 and the ISV pin3.

ISCU terminal 50 is the Starter signal (~12V active). ISCU reduces the ISV's air flow when starter is cranking.

Idle RPM should step up slightly when Power Steering Pressure Switch (LH) is active. Same with active AC (also ~12V active).

Try your oscope on ISCU terminal ST1. If you don't see a sq wave that's ~10V peak to peak, it might be related to that limited current ('26mA').
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zoti
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PostPosted: Sun Aug 29, 2021 1:23 pm    Post subject: Re: More idle control issues. Reply with quote

RawUmber wrote:
26mA is obviously out of spec, and might not be able to operate the ISV at that point. Is the amp meter hooked up correctly? It should be in series with the load (ie, ISV). Ex: between the ISCU ST2 and the ISV pin3.

ISCU terminal 50 is the Starter signal (~12V active). ISCU reduces the ISV's air flow when starter is cranking.

Idle RPM should step up slightly when Power Steering Pressure Switch (LH) is active. Same with active AC (also ~12V active).

Try your oscope on ISCU terminal ST1. If you don't see a sq wave that's ~10V peak to peak, it might be related to that limited current ('26mA').


I made a VW 1315a/2 copy. I tested one wire based on what I saw online. I will try the other wire.

26ma is definitely low but it does open the valve. I was expecting to see the valve vibrate but it just holds it open in a position which seem to raise the idle a bit compared to when the plug to the valve is disconnected.

This is the tool I made. I disconnect at the blue circle and connect the meter there in series.

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