Date: Mon, 3 Sep 2007 02:00:52 -0400
Reply-To: Tinkerman007 <tinkerman007@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tinkerman007 <tinkerman007@YAHOO.COM>
Subject: It's time to hit that idle Stabilizer on the head!!!
Hello Volks!
After a long while of idle and stalling problems after warmup in my 2.1L
European Digijet, with no solution from the dealer garage, I decided to
take it head on!
I thoroughly learned the system, and quickly found that both my throttle
valve switch as well as Idle Stabilization weren't working properly.
Resetting the switch seemed to improve matters, but still my Idle control
valve (ICV) wasn't humming as mentioned in the Bentley manual.
BTW, setting the switch as per bentley (0.05-0.1mm clearance) didn't work
because the switch wouldn't close reliably at idle, so I had to back it
off a little more.
And since the ICV was within spec (4.5 ohms) I dug in deep and found the
Idle Stabilizer Control unit behind the rear passenger signaling lights,
and quickly opened it up for inspection, daring to do so thanks to all the
informative posts on the list. That black box (and ICV) were always like
black magic to me, so I decided to end the magic and solve those
problems...I hereby declare war on the mystery of the ISCU and ISV!
First off I fixed two clearly visible problems - Corrosion on the external
connector pins and the disintegrating internal flat cable that connected
the two boards (one track was broken and also shorting to the adjacent
track).
Then I also took many close-up pictures so I could later continue to
analyze the circuit and even decode the circuit digram...
Inside it I found a double-board with 3 quad opamps (LM2902), a dual
comparator (LM2903), the power transistor everybody'd talking about (that
goes bad) and another power device (probably a power regulator), with
markings not visible because they're installed face down, as well as many
descrete parts like resistors, caps, diodes, zeners and small transistors.
BTW, my ISCU part number is 251 907 393C, made by VDO.
Thanks to the info I found on the list regarding the St1 and St2 outputs
that drive the ICV, I was able to continue the analysis and can provide
the following info regarding the connection pins (useful for testing it
standalone as well as reverse engineering it for the benefit of the list
memebers who want to save those 350$ (ouch!) and repair their defective
units:
Pin Pin
name in
STAMPED wiring
on
ISCU diagram Pin function
----- -------- -------------
15 14 Switched +12V from ECU power relay
LH 15 Power steering pressure switch input
31 5 Ground
ST1 11 Output1 to ISV (Transistor Collector?)
ST2 4 Output2 to ISV
1 17 Ignition pulses from Ignition coil driver
LS 8 Throttle valve switch input
T 13 Coolant temperature sensor (TEMP2) input
K 2 unused?
50 6 +12V while starter is turning
This is only the beginning, because I can provide my photos to the list
for a joint effort of reverse engineering project to get the schematic so
we can easily repair these expensive units (rememeber, 350$...ouch!).
Also, for debugging purposes, I need to know if the ISV indeed buzzes with
ignition on with motor NOT RUNNING as mentioned by members on the list,
because it has an input for ignition pulses (pin 1/17) and I'd expect it
wouldn't "buzz" without those pulses.
Can anyone shed light on that?
Thanks and it's a pleasure being a member of such a nice community.
Cheers!
