Idle Stabilization Valve (ISV), 88 5K

["Christopher Ritchie" <cjr1@gte.net>]

My car has mostly been idling around 1200 rpms.  This is after warm up and
without A/C.  Took off a gray cylindrical thing with 2 ports to vacuum and
one electrical connector.  It is on top of the intake manifold, at the
back.  It was marked:

	BOSCH

	0 280 140 512
                             
Made in Germany  (011)  12V

VW  034 133 455B

Cleaned it out with carburetor cleaner.  There seems to be another cylinder
inside which rotates.  After cleaning, it rotated pretty freely.  

Is this the ISV?  Car seems to idle lower, but I really did not get a
chance to run it much.  

The car also "jerks" at light throttle - on and off the gas.  This is
especially pronounced in lower gears in stop and go traffic.  I can also
feel it to a lesser extent in higher gears at higher speeds.  Maybe some of
this is driveline "slop", but does the ISV contribute to this?  I thought I
read something here about the ISV smoothing out the on/off throttle.  What
does the ISV do?  How much do they cost?  How does one test it?