Focus wagon idles rough when engine is warm

We have a Ford Focus wagon that idles rough once the engine starts coming up to temperature. When you first start the car it's fine. For example, today I started the car, drove it up the road to the store and it was fine, but upon returning to my driveway just a few minutes later, as the engine temperature was just starting to come up, it started idling really rough. The idle is so rough it sounds like its on the verge of stalling, but it never has actually stalled.

An oxygen sensor has been replaced and it was good for a while, but now the problem is back.

The check engine light is on as well.

Any ideas on what the issue could be? Could it be a case of the replacement oxygen sensor was faulty or is there something else going on?

Throttle clean interval should be at least 10k

i would get the codes checked on it to see what ecu says is bad. most parts stores and some shops will check the codes for free. write the code numbers down for reference. it might be a bad iac valve