IAC modifications

[bruce plecan]

In response to Mark Romans, what you discribe, as your problem is exactly
what I discribed as mine.
   As you mentioned there are three GMC pintle designs, and I tried them 
all before going to "my design".  It's beeen ages, but I measured the 
diameters, and lenghts and made a blueprint of the pintle itself.  I then
using drill bits measured the corresponding hole in the TB where the
pintle seatted (on some there is enough of a carbon pattern to make this
measurement).  I beleive the thread is a 6-32.  I then figured on using
the hole size as the mid diameter for the pintle.  From that I added, and
subtracted .005", so that the total taper was .010".  Once I got the
new "cones" (pintles) from the machine shop I unsrewed the OEM ones, and
threaded the new ones on with loctite.  I then experimented with 
resetting the min idle adjustment, and reset the TPS at each new min 
opening.  I didn't try tampering (or could I) with the ECM min idle speed
Once I had the hot idle right, I then using a file, and electric drill
cut a new taper to the pintle.  If you have a scanner, you can read what
your cold engine IAC count is.  If you also have one of the stepper motor
experimenters controller kits, with the old TB, you can play to your 
hearts content on tapers, and such.  After several (read numerous) you
can get your perfect cold idle speed, and have a very stable hot idle.
I orginally had 4 made since the cross-fire I was dealing with uses two
at a time.  Once I had a pattern, I then did a fine copy, for use.  Mild
steel was fine for the material, no need for stainless, since they 
quickly carbon-over.
  Hope that better explains it.  Bruce