Re: Idle Stabilization Valve correct operation

[Phil Rose <pjrose@servtech.com>]

Steve manning wrote:
>>While waiting for the oil to drain, I decided to pull my ISv and take a
>>gander.  It too, is opened just a crack; maybe a dime's width (not a
>>nickel) - can't really get the calipers in there<g> but it is opened.
>>De-fibbing with a 9V pops it open smoothly to almost completely open (just
>>that dime's worth closed).  Removing power snaps it shut again.  So, it
>>seems to be opening/closing the "full amount" with the initial and ending
>>positions being "off".  BUT, doesn't there need to be some air going
>>through?  I couldn't find any other bypass so I'm confused now.


Steve, are you saying that the ISV was a little open ("dime's worth") when
you initially examined it, but then--after doing the 9V "defib"--the
resting (or "off") position was able to come to fully closed? In which case
I gather that early stages of gunk can have the effect of allowing in a
little unwanted air "leak"  in the nominally off position. Does this tend
to happen because the ECU often doesn't reduce power in a discontinuous
manner (i.e., a "step-function" to zero volts) like the 9V defibrillation
does?

As some ISV gunk begins to accumulate, there must be an increasing chance
that--on startup--the ISV will cause the idle to be a bit (nickle or dime's
worth) too lean. I will definitely do an ISV cleaning today as I'm sure
I'll be finding the same "not-quite-OK" operation.

BTW, no 200Q20V people have responded about my claim that I can detect a
significant increase in idle speed if I _re_connect my ISV while the engine
is running. Idle drops when I pull the plug, increases when I connect, etc.
I thought the ISV would act "dead" unless the engine was switched off and
then restarted. I recall my '89 100 needed to be restarted for the ISV to
work after reconnecting. I guess the 3B Motronic is "different" in this
respect?

Phil

Phil Rose				Rochester, NY
'89 100 (For Sale, 111K, automatic)
'91 200q				mailto:pjrose@servtech.com