Rough idling/loping at idle it otherwise runs fine off idle.

run fault codes
check for dirty injectors

The rough idle is associated with the p011 code. The P011 code is: Camshaft A over advanced. There is a mechanical fault with the intake camshaft.
You need to take the car into a mechanic, preferably the dealer since they have all of the needed special tools, to properly diagnose and repair the issue.

Idle air control (IAC) control rpm idle during idle.

Test it on idle with ALL electrical on full force.
RPM should increase.
If RPM remain the same then IAC is question.

Clean your throttle body and map/maf sensor. If that doesn't work you may have a bad iac sensor (idle air control sensor)

Check for vacuum leaks

You never replace anything, on a Wishing,Hoping,Pushing,Poking,diagnostic approach

You learn the vehicles Systems,Test,then Replace,if you have a failed component.

Work on the Misfire Issues.
Then you lean O2 Codes will go away.

Not a the plugs.

Think lean---Vacuum leaks,EGR Valve leak,EVAP System leaks,anything with a hose that lets air into the intake system.
Exhaust System leaks,near sensors

Probably a bad idle air motor, it controls idle electronicaly

I think your 88 mustang contols the fuel air mix with a manifold absolute pressure sensor. Ive seen were the vacume line going into one has worked loose or broken cousing rough idle and throttle. llso check that the idle air control valve isn't plugged up with soot. This would also result in rough or loping idle but would be fine once the engine is hot. Let me know if this was helpful, good luck.

check the air filter and spark plugs and wires

oxgen sensor needs replacement this controls the air flow