Don't just throw parts at it.
Clean the IAC, see if that helps. One way to check it is to remove its electrical connector while it is idling. Listen for an idle change. No change=bad IAC.
IAT is also testable, but I don't know its ohm range. Simply remove it, attach an ohmmeter and heat it with a hair dryer. If its ohms vary with temp change, it's probably good. That year Focus, IAT MAY be integrated into the MAF, should you be unable to locate it on the intake tube.
You might also clean the MAF, check/clean/gap or replace the spark plugs.
2000 2.5 MO5D 4.10 one-wheel drive DD - gave to my older son
1990 STX 87 2.9 going in.....Junked it
2000 3.0 4WD M05D 4.10 S-cab Off-Road package with 235-75-15" tires, hotrod DD, lol