I have a 6 cyl auto EF which recently started idling too high. When starting, the engine idles (in park) at about 2000rpm for about 2 seconds then gradually drops back to normal after about 4 seconds. It does the same when stopping completely after driving - initially 1000 rpm for about 3 secs, then slowly dropping back to 700rpm after another 2 seconds. I changed the ISC solenoid with another EF, but no change. I checked the voltage to the ISC solenoid which is 13.6v with ignition on. I removed the plug to the ISC and checked the voltage with engine running - 13.6v. After turning a/c on then selecting drive, the result is 13.2v. With the ISC disconnected, the car appears to drive normally - the only problem is that when you are in park, if you turn a/c on & select drive the revs drop momentarily to about 500rpm - which I can understand. I checked the operation with an AU Fairmont which works normally, but if I disconnect the ISC on the AU (the AU calls it an IAC valve) the engine stalls instantly.
Any ideas?

The signal to the ISC is pulse width modulated, checking with a meter is not going to give you a correct indication. I would try resetting the base idle first, then proceed with the ISC cleaning procedure widely documented on this site.

Thanks for the advice. I will reset base idle as you suggest.

I would also suggest cleaning the ISC with some nail polish remover.. they do gum up from time to time. had the same issue, but only on 1 of my last 3 fords.

Thanks guys for your help. After resetting base idle, the problem was solved. I also cleaned (as suggested) the ISC, so hopefully no more problems.