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I had problems with the Idle Stabilizer Relay on my 1984 80q a few
years ago, and here is what I found out.
The relay drives the valve with a varying mark/space ratio signal which
controls the amount by which it opens. You really need a scope or a
dwell meter to see this. The frequency of this signal (from memory)
is around 4kHz. If you apply 12V to the valve, it will open fully
(engine revs could approach >3000). Fuel injection specialist books
(and maybe the Bentley) give information on the mark/space ratio
expected for correct idle on a warm engine.
Signals which controlled my relay (yours may be different) were:
engine revs (distributor signal in my case)
engine temperature (NTC thermistor) (causes higher idle when cold)
throttle closed switch
There were more contacts on the relay, but they were unused in my application.
Things worth checking are the throttle closed switch, the throttle
mechanical bypass screw (if screwed in too much, the revs might drop
very low before the idle stabilizer got a chance to sort things out -
this could cause a stall.
Also, it is possible that this problem is nothing to do with idle
stabilization. I had a K-Jetronic Jetta that vapourised the fuel in
its fuel lines whenever it was stopped for a few minutes - the
symptoms were that it was sometimes difficult to hot start, would
often cut out, and would idle very badly for 30 seconds or so - after
that it was fine. The solution to this problem is to try and get rid
of some underbonnet (underhood as you probably call it) heat. Extra
injector fans, better engine oil, new radiator etc can solve this.
Also check your fuel accumulator and fuel pump check valve - if these
let the pressure drop, vapourisation in the fuel lines is more likely.
Sorry I can't be concise and say "the problem is your ...", but with
these wretched cars, things are never that simple.
1983 Avant CD
>From: "Al Powell" <APOWELL@agcom.tamu.edu>
>Date: Wed, 22 May 1996 12:09:49 CDT
>List-friends, my 1990-200 has started to die when it's a) fully warmed
>up, then b) sits for a few minutes and c) is re-started.
>In this scenario, when I re-start it, the darn thing dies every time
>I let the RPM's drop....but only for about the first 2 or 3 minutes of
>driving. After that, it's fine and will idle OK. Of course, I suspect my
>friend and ours, the much-fabled Idle Control Valve.
. . . (stuff deleted)