Need help with setting the correct idle. (auto trans)

What should the correct idle be when engine is at normal operating temp :

In park

In drive

Had problems starting, so my mechanic adjusted the idle too high, at 1300rpm
(by adjusting the 2 nuts on the throttle cable), & maybe some other adjustment.

That solved the starting problem, but was idling too high at 1300rpm.

Got check engine light, codes are idle control malfunction and knock sensor.

Told mechanic to put idle back to 800 rpm.

Now it starts fist time in the mornings, but I NOTICE on cold starts needle goes to 800 rpm and stays there ( still CE light is on ), am I right in saying, on cold start needle should go to 1300 initially, and then gradually come down to 800 rpm as the engine warms up to normal temp.

If I can get the idle put back to what it should be, hopefully that will take care of the CE light, without starting problems.

Is setting the idle fairly easy ???