Stumble / Miss on '92 Corolla (4afe?) Troubleshooting help?

[Backtobasics]

I just bought a 92 Corolla, 4 door, auto.
I believe the engine is referred to as a 4AFE.

225K miles, interior is impecible, engine runs and pulls pretty well but the stumble.
SEARCH feature did not give me any apparent answers...but I tried.
Previous owner said he "checked" the plugs, and they replaced the distributor and wires with another distributor (also used). The car has issue where the idle randomly changed, either in park, or low throttle. Once up to speed it is fine with NO hiccups. Underhood is pretty clean, and I do not see any unhooked vacuum lines, etc, so it appears to be pretty stock.

We are going to clean the throttle body, check out plugs and wires, etc.

Can someone give me a general direction as to where to start looking after this? Idle air control seems to do its job by correcting idle, but in will move up and down and then go smooth for a bit. EGR valve / Throttle position sensor / IAC / ?

[90 GP]

Start with checking for stored trouble codes. They could be stored but not trigger check engine light. The link is below. Also check a manual for troubleshooting the throttle position sensor. If you register online at Auto Zone you can access their free online repair manuals for troubleshooting parts. With that mileage if it's the original engine check engine compression and the timing to be sure at spec.

http://www.troublecodes.net/Toyota/