Date: Sat, 9 Oct 2010 19:54:03 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: It continues - Engine RPM Hunting 200-500 rpm
In-Reply-To: <4CB0F30C.8060007@charter.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 05:56 PM 10/9/2010 -0500, John Rodgers wrote:
>I disconnected the idle stabilizer valve after warm up, and restarted.
>It was a little rough to start, but after start-up it smoothed out at
>1000 rpm like before, and still would not run properly between 1000 and
>2000 rpm.
If it's idling fast with the ISV out of circuit, then the idle is set
too high. The ISV can only raise the idle, never lower it.
>I have not disconnected the O2 Sensor yet. O2 sensors have caused rough
>running on my other vans, and smoothed out when disconnected, but this
>is a little different.
My personal recommendation, at any sign of trouble *start* by
disconnecting the O2 sensor. It has no function in the correct
operation of the motor; it is only there for reasons of emissions
control. It is entirely capable both of causing and of concealing problems.
>So apparently, this takes me to the throttle switch - I think. But this
>engine has only 114,000 miles and is clean, so I'm suspicious about
>whether it's the switch or not. Never tampered with the switch before,
>so a little unsettled about working on that.
Don't touch it! *Test* it. If it's bad, *then* touch it. If you
*do* need to touch it, take off the throttle body, open up and clean
up the switch, adjusting cam etc. so that you can adjust it without
wrecking it. Adjust it off the vehicle. If there is too much wear
in the bore (and being unable to set the idle low enough would be a
strong clue) it may be necessary to set the switch while installed
and engine running.
>Any input on this would be appreciated.
The idle circuit isn't the [main] problem since problem remained with
it disconnected. 1000 rpm idle is either throttle body wear or
misadjusted base idle, possibly an attempt to alleviate the problem
you're having. You've got three vans...easy to swap out ECU, AFM,
T-II. Without being rigorous, it seems to me that if O2 is
disconnected and all three of those swap out without solving the
issue, that points to air leaks or wiring. Once you've got it to
where it runs properly with the ISV out of circuit (i.e. correct base
idle that dips with load changes, but otherwise everything good on a
warm engine) then you can determine if the idle circuit has problems.
Yours,
David
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