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Re: increasing idle

   We have a 87 5000tq that over the past two years has been gradually
   increasing its idle speed. What happens is that when you start the beast
   up in the morning it runs fine, the idle sits at around 800 rpm, this is
   with climate control set to econ not auto, after the car warms up. After
   driving the car around, say for couple a minutes or more, and then
   coming to a stop the idle speed settles at around 1100 to 1400 rpms,
   it's inconsisten as to what idle speed it settles at but it's always in
   that range. Also after prolonged running and then coming to a stop the
   idle speed bounces around, up to 1500 to 1600 rpm before it settles at
   the high rpm rate. Sometimes the rpm bouncing will go through three or
   four iterations before it settles down to a steady state.

'dunno if the '87 models still have this, but earlier models had a gizmo
called something like the Auxilliary Air Valve. This was a "static" idle
adjust to allow extra air into the intake when cold. It has a small heater
inside to warm it up and close off the extra air, so it has two (or more)
wires leading into it.  On my car, it's at the back end of the head, next
to the A/C aux air valve.

Failure of this gizmo would cause exactly your observed symptoms -- an
increasing idle speed as the engine warms up (when the AAV is supposed
to be heating up and closing off in parallel).