Date: Sun, 10 Apr 2005 08:34:47 -0400
Reply-To: Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: Throttle valve switch, checking/adjusting
In-Reply-To: <20050409191846.61347.qmail@web81407.mail.yahoo.com>
Content-type: text/plain; charset=us-ascii
The surging at idle is actually a sigh the throttle switch is working.
If it wasn't closed when the throttle is closed the surging wouldn't be
there. Now, why is it surging?
The design works as follows:
When the throttle is closed, if the engine rpm goes over ~1,300, the
injectors are turned off. This usually applies during deceleration or
going down a hill. During this Deceleration, the O2 sensor is going to
read an extremely lean condition. When the engine rpm drops and injector
operation is resumed, the O2 sensor is ignored for 30 crankshaft
revolutions. This will cause to engine to idle at a higher than normal
speed if the airflow meter is not working properly. If the higher speed
gets it near 1,300 rpm, the fuel is cut off, (the drop), and then when
it turns back on, the creep up and the cycle goes again. Here is the
surging.
The surging can also be caused by a vacuum problem to the distributor
advance mechanism. Especially on the retard side and a weak advance
spring will contribute to this.
The fix:
Check all the basic settings. Especially the throttle stop. The throttle
must be able to close almost completely. Idle speed adjustment is done
with the bypass screw. Adjust the stop to keep the throttle from
sticking closed. Make sure the ignition timing is correct. Set with the
idle stabilizer bypassed. Make sure the retard side of the diaphragm is
getting a good vacuum signal. Connecting with a tee to the fuel pressure
regulator vacuum hose work best.
Check the idle mixture adjustment. Disconnect the O2 sensor and connect
a volt meter to it. Start the engine. With the engine at idle speed,
adjust to .5 volt or slightly less. Idle speed should be ~850-950 rpm.
You also want to check the auxiliary air regulator. Make sure it is
getting power and that it is closing quickly. It is common for these
engines to surge after warm restarts. This is due to the air regulator
providing a fast idle even if the engine is going close loop.
Hope this helps.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Wognacious
Sent: Saturday, April 09, 2005 3:19 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Throttle valve switch, checking/adjusting
Howdy,
I hope everyone is having a great Saturday either driving, camping or
tinkering with their beloved Vanagons. I, however, am having a bit of a
delimma. I posted earlier in the week about getting back from an 800
plus mile trip to Oregon last weekend and that after the trip I was
experiencing a surging idle at low RPM's. This is after the engine warms
up. So I'm checking out the throttle valve switch doing the tests
described on page 24.35 of the Bentley. I have the single switch
obviously. What isn't getting through my thick skull is the feeler gauge
adjustment screw stuff. By loosening screw 2 and adjusting screw 3 I see
no movement between the idle stop and the idle adjusing screw. I can
turn it both ways to the max and see no gap closing or opening. I'm
obviously missing something here. Any insight would be greatly
appreciated.
Thanx,
Paul Rogers
85 Westy
