Date: Sun, 17 Aug 2008 23:06:28 -0700
Reply-To: John Bange <jbange@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Bange <jbange@GMAIL.COM>
Subject: Re: Idle Relay - Idle Valve match?
In-Reply-To: <040301c9001e$5a265410$6800a8c0@4BYCY41>
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> I did swap out the idle relay (controller) and it acted exactly the same
> way.
Heh. Well, then I betcha' THAT'S not it! Back to the drawing board...
> Anyone (who knows these relays) think it might be a bad connection, wiring
> or a ground? I cleaned things up pretty well, but it's always possible to do
> more.
I'd say that grounds are ALWAYS a suspect when you have weird
electrical "Heisenbugs". That was one of the alternate theories that
occurred to me today.
> Why would it act up when it gets warmed up, but be OK when cold? It gets the
> signal from the temp sensor obviously.
Indeed it does. The idle controller has the following connections:
RED/BLK - power from ignition switch
RED/WHT - power from fuel pump relay
WHT/YEL - power steering high pressure switch
BRN - ground
GRY - coolant temp sensor
RED/BLU - throttle valve switch
WHT - output to idle valve
YEL - output to idle valve
GRN - hall generator (RPM signal)
The unit does indeed watch the coolant temp sensor, so that's always a
possible source of trouble. A marginal connection could cause the
trouble you describe. Excess resistance on the wire wouldn't affect
the behavior of the idle controller when cold, as the temp reading
starts off below whatever minimum "cold start idle adjustment"
threshold there is; but as it warmed, the idle controller would
perceive it as still being cold, perhaps even intermittently, causing
excessive idle air bypass. A quick check of the gray wire should tell
you if you have a resistance problem.
Another possibility is a gummy idle valve not responding fast enough
at certain ranges of opening, but that one seems unlikely.
Probably not what you have going on, but worth mentioning: I once had
a weird idle surge issue that turned out to be a loose distributor
collar bolt, which I'd forgotten to tighten after adjusting the timing
last. As I recall the distributor had "migrated" almost 10 degrees
off...
> Does anyone have a diagram of what's going on inside this relay?
Well... I kinda have one, but it's not complete and what I do have
ain't pretty! "Relay" is really the wrong word for it. It's actually a
hand-tuned analog computer. It's the sort of device electrical
engineers used to stay awake at night thinking about, before the
advent of digital microcontrollers made solving such problems trivial.
Imagine, if you will, designing a machine to keep an engine running at
one of three or four predetermined numbers of revolutions per minute,
with neither the ability to explicitly count revolutions, nor mark the
passage of time. It's beyond me, it is.
--
John Bange
'90 Vanagon - "Lastwagen"
'90 Vanagon GL - "Wiesel"