I'll say what I can on this, though I'll defer to the experts here...

It sounds like your van is running ok as long as it's in open loop mode
(that is, when you first start it, the ECU ignores the information from all
sensors until they reach a certain temperature.) This takes a few minutes
from cold start, approximately the time you're describing. The problem
begins once the ECU starts to factor in the sensor information.

That tells me the problem is either in one of the sensors or in the circuits
going to the sensors.

The first ones I would check would be the O2 sensor (disconnect it when warm
and see if the condition changes) the Temp 2 sensor, and the AFM. You might
have your mixture on the AFM reset by a professional and see if that helps.

If you're handy with a multimeter, there are several tests you can run from
the connector that goes to the ECU. They're well described in the Bentley
manual.

Check in again if you have other questions. What you're describing could be
a ton of things but this may give you a start.

Geza

On Mon, 18 Jun 2007 00:14:03 EDT, - Jeff & Kim Prudhoe <Jkpvw@AOL.COM> wrote:

><HTML><PRE><FONT FACE=arial,helvetica>My neighbor just purchased an '87
Westy that has the following problems:
>
>From a cold start the van will idle for 4-5 minutes at 900 RPM before
>stumbling and stalling out.  The tach would spike to 2000 RPM just before
it stalled.
>
>From a cold start, in city traffic, the van will stumble and stall
>frequently.  This occurs after backing off the throttle or when at a
traffic stop.
>
>Yesterday we took it on the interstate (10 miles) where the van performed
>without incident.  After getting off the ramp and back into city traffic,
the van
>did not repeat the problem.  We drove it to the house and let it idle for 10
>minutes without a problem.
>
>Today, the owner took the van back on the interstate for a 30 mile run.  As
>before, during the drive to the interstate, the van demonstrated the same
>issues.  Again, after the short highway trip no problems were experienced.
 From
>the interstate he drove to the grocer where the van sat for 25 minutes.  On the
>way home the van began to stumble again during low speed (2k RPM) operation.
>
>These events occurred both with and without a new idle stabilizer valve (new
>owner purchased before talking to me) and a newer functioning idle stabilizer
>unit that I swapped from a good running van.
>
>Could this be a coolant temp sensor?  Was 25 minutes of down time enough to
>trigger a cold start problem?
>
>Any thoughts are appreciated.
>
>Jeff Prudhoe
>           <BR><BR><BR>**************************************<BR> See
what's free at
>http://www.aol.com.</HTML></PRE></HTML>