IAC might be filthy, can cause starting and idling issues, if you have never cleaned it it's a place to start, carby cleaner works pretty well, stuff a clean rag in the TB so the crud doesn't get into the engine.
Seafoam is great. Ill have a look tomorrow and see if I have some in the shed, as it sounds like one of those odd things I would buy.
This is only my opinion, so be kind
May I ask how a good tune can prevent oil rich air being returned to throttle body.