Date: Thu, 16 Oct 2014 17:57:46 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Weird "idle" problem
In-Reply-To: <080301cfe960$824a66c0$86df3440$@gmail.com>
Content-Type: text/plain; charset="us-ascii"
Let's start with the basics. The most important tool in troubleshooting is
knowing the "process" and how it should work when things are normal. The
idle stabilizer valve is an "add on" and it is there to help compensate for
some variables most notably the O2 sensor, warm up, and load changes such as
the alternator, AC, power steering, and the automatic. For years many cars
operated with all of these accessories without this complication. Once warm
your engine should be able to start, run, and be drivable without the idle
compensation system even being there. As for the throttle switches on the
Vanagon they are there for only two reasons. Closed throttle if the engine
is being overrun such as coasting or slowing in gear at some speed the
injectors will actually get turned off until the engine drops down to some
lower point. This seems to be about 1,300 rpm on the 2.1. At full throttle
and the AFM has flow indicating acceleration or load the fuel mixture is
richened slightly and the O2 sensor ignored. This gives us a tad more power
and helps to keep pistons and valves from burning. Oh, on the idle part as
the engine slows down and the injectors turned back on the O2 sensor is
ignored for a short time as it would be indicating very lean causing an over
rich mixture until it can get control again.
Now based on the above the first step is to get it warm and get the basic
settings adjusted so that the engine can idle with the valve disconnected.
Set for about 750-800 rpm this way. If you can't do this you have problems.
While doing these adjustments disconnect the O2 sensor also to remove that
variable. Now if reconnecting the valve causes the run-away you have to
check some wiring to make sure the temp2 sensor and other signals are
getting to the controller. A bad valve, (coil or spring) or the controller
can cause the run-away. A duty cycle meter or amp meter are the methods to
determine if the controller current is out control or the valve opens up
without being told to. The valve pulses, (hums) as the controller varies the
valve by changing the percent of time it provides current.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Stuart MacMillan
Sent: Thursday, October 16, 2014 12:45 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Weird "idle" problem
Just got my son's "new" '87, and we were told by the seller it had an idle
problem. He's driven it about 200 miles with nothing more than a bit of an
idle surge once in a while, but now it won't idle at all cold, and when it
warms up for a couple of minutes it races up to 3000 rpm and stays there.
Restarting doesn't help, and only when I unplug the idle control valve will
it stop (die).
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!
The only way to test it is to replace it for $200.
Thanks!
Stuart
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