Ford EEC4 timing and idle control question

[olddog]

I have observed that when the engine was reved up and returning to an idle, that the timing drops back to the base setting (10*), as it settles to normal idle.

I don't know if I read this or assumed as much, but I thought this is basically to duplicate what ported vacuum did on the old vacuum advance distributors, which was done to reduce emissions by keeping the combustion chamber hot.

Now I had someone claim that the EEC4 uses timing to control the idle speed. I thought that is what the IAC does, I said. The reply, it uses both. The timing has a much faster response. Then he said in my case the idle is set up to 900 rpm and the ECU is trying to control at 600 or so. So the IAC is staying closed and cannot get the rpm down to setpoint. Then it pulls all the advance out to try to get idle rpm down to setpoint.

Ok the argument sounds logical. I have read a fair amount on the EEC4, and I have not heard anyone else mention timing is part of the idle rpm control strategy.

Can anyone tell me if this is true or false?