Thanks David, I've also been told to check the timing again, it could be a
bad hall sensor.  So, is that cover on the brain easily removed?

-----Original Message-----
From: David Beierl [mailto:dbeierl@attglobal.net]
Sent: Thursday, October 16, 2014 3:23 PM
To: Stuart MacMillan
Cc: vanagon@gerry.vanagon.com
Subject: Re: Weird "idle" problem

At 12:44 PM 10/16/2014, Stuart MacMillan wrote:
>I've checked the TPS with an ohm meter and it works fine, and the idle
>valve hums.  I can't find any vacuum leaks (propane torch probe), and
>it was recently tuned up.  So, is it possible for a bad Idle control
>unit to cause this?  It seems odd that an engine can run at 3000 with the
throttle closed!

Stuart, the idle controller is subject to solder fatigue just like the ECU,
and it has a lot fewer joints to reflow so it's well worth it to simply
reflow everything rather than trying to find a 35X stereo scope to really
look hard at the joints.  You have to add a bit of clean 60/40 or 63/37
rosin core solder to each joint, and if you end up with too much use a
soldersucker or braid to remove it and redo the joint.

Even before doing that, remove and replace the controller.  You can look for
corrosion on the terminals, and replugging it will exercise the connections
nicely as the Faston type terminals have good scrubbing action.

Yours,
David
ps -- I have long ago seen a Jetta with a sticking idle valve cycle up to
2500 rpm and back every few seconds.  I presume that its idle controller
kept advancing the power until the valve unstuck, at which point it jumped
up.  Cleaning with solvents cured it, at least for the moment.  Your
symptoms do not sound like this if you're describing accurately, but rather
a valve that's being actively driven to stay open.