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Date:         Wed, 5 May 2010 10:45:52 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: 84 Westy stumbles off idle
Comments: To: Geo <ahwahneevw@GMAIL.COM>
In-Reply-To:  <w2y32db11c91005050657ma206cfa2l489cce5e78bfc377@mail.gmail .com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Dear Geo,

At 09:57 AM 5/5/2010, Geo wrote: >84 Westy, 1.9L, Manual --

Ah, thank you :)

>I can recreate the problem in the driveway just pressing the pedal at >different rates, thus it seems independent of the demand on the engine when >the clutch is released.

Ok.

>I'm pretty sure I have those throttle micro-switches correctly adjusted >though I even tried some incorrect settings to see if that mattered -- it >didn't.

Run a temporary pair of wires from the switch wires up front and put a small yellow LED across them. You should see off or dim at closed and full throttle, and bright everywhere else. This will tell you for sure if the idle switch is working correctly. If it isn't spraying some contact cleaner in where the rubber boot is may cure it.

>I do not have a spare idle stabilizer (that green dingus over on the left) >and have not tried the trick of disconnecting the stabilzer and connecting >the plugs together -- if that makes a difference what would it tell me?

Without the idle stab it will be a bit easier to stall when setting out and the idle will change a bit when various loads on the engine change, but it should be perfectly drivable. If that cures the problem, you've got your culprit. I dont expect it will, but it might -- that dingus fiddles with the timing at low rpms.

Vacuum leaks can be hard to find -- a particularly hard one is the two studs in the manifold that secure the cooling pipe across the top. It's surprisingly easy to rip one of them out and it's invisible unless you go pull on the pipe.

I have to wonder about a worn spot in the AFM wiper. With an analog voltmeter set for five volts and the power on, you should be able to slowly move the vane by hand and see the voltage vary smoothly and monotonically, i.e. it never drops when it should be increasing. A meter that responds quickly makes it much easier and an oscilloscope will show you noisy contact that the meter will never find. Normal digital meters respond much too slowly to be useful for this.

I wonder about vacuum advance/retard on the distributor.

This is a long shot, but enrichment for acceleration is provided by inertial overswing of the AFM vane. If it's somehow gotten stiff that could give you too lean a mixture on quick acceleration, especially at low rpm/airflow.

I *always* wonder if the O2 sensor could be misbehaving, so disconnect it -- if the engine is in reasonable tune it will run just fine without it, and it might be masking another symptom as well. When everything is good, hook it back up again.

That should keep you busy until someone who actually knows what he's talking about gets involved. <g>

Yours, David


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