Hi,
Sounds very random but I gather it’s almost dialed in to running nicely?

While you are under the hood be sure to check the accordion hose behind the AMM.
You might have a tiny pin hole in the volutes somewhere or the ends are not sealing under the clamps.

With the twisting of the engine a pin hole or slit can randomly open up and throw off the Idle mixtures.
Mostly this happens in town driving and the engines will get rough or out right die.
Use a cylindrical light up in the middle and flex it.

I haven’t followed but make sure the throttle plate and cables are not sticking and how old is the IAC valve.
Idle Air Control.

Check other vacuum hoses around the throttle body and down to where ever the evaporative canister is for emissions purposes.
It has a valve with two hoses and on 240s they rot.

Does your car have a Exhaust Recirculating valve?
If the EGR malfunctions it can cause idling issues but it will usually throw a code.
How is the CEL (check engine light,) anything?

Phil