Date:         Sun, 20 Apr 2003 23:11:02 EDT
Reply-To:     Wolfvan88@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Robert Lilley <Wolfvan88@AOL.COM>
Subject:      Getting a handle on Idle problems...
Content-Type: text/plain; charset="US-ASCII"

I think that if one understands what each part does and how it interacts with
the idle system, that one can be better able to fix problems.  This goes for
the rest of the FI components.

The Idle control valve:
- Is simply a fan that pumps air into the center plenum.
-The volume is metered by the airflow meter.
-The volume is determined by the idle control module.  The increase or
decrease in speed based on out puts from various sensors.


The throttle body:
-passes a determined amount of air past the closed butterfly due to its
factory settings.
-The big screw in the throttle body allows for additional volume of metered
air to pass.
-Has the throttle switch sensor
                Digifant has a single throttle switch mounted on bottom.
                Digijet has two switches mounted on top


Air flow meter:
-The screw in the air flow meter allows for UN-METERED air to pass into the
idle circuit.

Throttle switch:
-When throttle is closed it turns control of the idle over to the idle
control module from the ECU.


O2 Sensor:
-gives feed back to idle control module as to correct amount of fuel during
idle.
  (is it Ignored at idle and the amount of fuel is based on metered air flow
and temp II readings?)


Fuel pressure regulator:
-at idle it should be around 29 PSI (+-3 PSI)
-vacuum hose is in good shape


When I have tried to increase my idle speed by turning out the screw on the
throttle body, it increases RPMs, but then after a few moments it drops back
to 880. When I turn the screw in the RPMs dropped, but after a few moments
the idle goes back to 880 (I even turned it in completely closed).  Increase
timing and engine RPMs increase and in a few moments it drops back to 880.  I
checked the readings from O2 sensor and it was running rich    It has got me
thinking that the idle control module keeps the idle to a factory setting and
it uses the sensors to get to that setting.  The idle control valve is adding
a set amount of metered air, it is running all the time at a certain rpm,
during off idle rpm.  During idle it either speeds the valve up or down
depending on needs.

I had to turn the screw on the AFM out about seven turns to get the O2 sensor
to drop to .6 during idle.  In reading the Bentley, the two screws are for
setting the correct CO level.  I might be getting too much air past my
butterfly valve after I took it apart and polished the rough inside, then
allotted for by the ECU that is affecting my HC at Idle.  Too much metered
air Vs UN-metered air.  The idle control valve could be running slower to
keep the RPMs at the factory specs due to the measured amount of air flow but
cannot add enough air to match the fuel amount so it runs rich.  I will do
some more checking Monday.

If your idle is running rough check:

That your injectors are not leaking
You do not have any vacuum leaks
Your temp 2 sensor is in specs (the one that measures coolant temp)
You do not have exhaust leaks at flanges or holes in pipes.
Cap and rotor are good
Plug wires are good check the resistance! I had new looking wires that tested
bad.
spark plugs bad
your fuel pressure regulator is good
AFM: air Temp sensor in spec AFM is OK
Grounds in Engine compartment OK
air filter not too dirty
compression low in one more cylinders
coolant leaking into exhaust
Idle control valve is dirty-clogged up, not turning correctly
Idle control module not working correctly.  If your AC works, test by turning
it on and seeing if idle stays steady or increases under load. If not check
wire from AC clutch plug to Idle control module. THIS assumes that the valve
has been checked and is OK.

There are other things to check, but cannot think of any anymore, my brain is
tired...

Robert