My 1989 Ford Taurus wagon with 3.8L engine started to idle at
2,500-3,000 Rpm soon after having the heads replaced last year. The idle
speed control valve was replaced because the bellows was damaged. No
change! Replaced the
ECA twice and still no change. Checked resistances to ground, +5V, +12V,
on all 60 ECA pins and found no abnormalities-shorts/opens. The coil
resistance is 10 Ohms which  is in my opinion rather low but the same as
the old units'. Voltage on the low side is 10V and at the high side is
battery voltage. Obniously 2-4V  across the coil is insufficient. The use
of a current boosting circuit-an emitter follower transistor-reduced the
idle speed to +/- 600 Rpm, but the valve never opens, causing the engine
to stall. An alternative method using a plate with a small hole between
the ISC and manifold works but this is not fixing the underlying problem.
  I've beeen climbing the walls for about a full year. Ford provided no
assistance at all. "Just Answer" also provided no solution. I'm at the
end
of my rope and ready to give up. This is something I have never done in
more than 60 years of servicing cars, TVs. audio, etc. Is someone able to
help?
Please help, Richard