Date: Wed, 17 Apr 2002 21:24:36 -0500
Reply-To: John Rodgers <jhrodgers@MINDSPRING.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <jhrodgers@MINDSPRING.COM>
Subject: Re: Idle speed, racing engine
Content-Type: text/plain; charset=us-ascii
Karen Gritis wrote:
>
>
> I wouldn't know what to do if it started the uncontrolled
> revving again on the way to the shop.
>
> Does anybody have any idea what's going on with my vanagon?
>
Karen, what you experienced can be frightening to the un-initiated.
You didn't mention what year your van is, but here is the scenario on my 88
GL with the 2.1L WBX engine. I know at least all the 86 and later vans are
this way.
There is an idle stabilizer control (ISC) and an idle stabilizer valve (ISV)
for the engine. When the engine is cold, the ISV which is located right on
top of the engine, operates to prevent the engine from stalling. Once the
engine is warm, the electronic brain called the ECU, located under the back
seat ( it a boxy looking thing), senses the warm engine via a temperature
sensor and cuts the ISV out of the circuit. From that point on the ISV
doesn't do much except sit there. However, there are a couple of conditions
under which the ISV in conjunction with the ISC (which is located in the
right rear of the van, inside the body, behind the right hand tail light
fixture) work to gether to keep the engine idling under a load.
1) Cold engine - ISV/ISC keep the engine idling until warmed up.
2) Air conditioner on - When the AC is on, two things happen. (a) the
radiator cooling fan will come on and stay on as long as the AC is turned
on. (b) The AC connection to the circuit will cause the ISV & ISC to kick
the engine idle up to accomodate the added load caused by running the AC.
I have seen so called mechanic's mystified by this arrangement. The first
place one has to start to get this system adjusted properly ... assuming
engine timeing and a number of similar things are within operating
parameters, is to get the idle speed properly adjusted. Some people don't
understand about the ISV, try to adjust the idle set screw, and get things
all screwed up. The the engine doesn't idle correctly for sure.
The engine should be cold. Start it, and feel the ISV. There should be at
least the slightest vibration. Stonger is OK. None is suspect.
Allow the engine to warm thoroughly. Then turn off the ignition. ,
Disconnect the connector on the end of the ISV. That disengages it from the
ECU circuit. Start the engine. Should idle about 900 rpm.
On the throttle body is a large flat slot-headed screw that is the set screw
for idle. Adjust right or left to raise or lower the rpm. Should idle around
900 rpm. If not, adjust accordingly. Once set, turn the engine off,
reconnect the ISV and restart the engine. The idle speed when warm should
be about 900 to 950 fro smooth idle.
Now turn on the AC. If all is well, the ISV/ISC circuit will kick the idle
up to 1200- 1300 rpm to support the added load of the air conditioner..
Thats about it. If that doesn't do the job, you have another problem
somewhere that will require more exhaustive tests and trouble shooting.
Good luck.
John Rodgers
88 GL driver
