Random Idle Speeds

89' 4.0L
The idle speed is rarely what it should be. Some times it stays at close to 1000RPM's sometimes at 750RPM's and some times it starts to falter lower than the 500RPM mark. I dont know when the throttle body was last cleaned if that is even a factor. What do you guys think? any sensors to check? or clean? What would be the first thing you would check or clean? or replace?
Let me know
TIA!

Pull off the throttle body and clean it with a spray can of carb cleaner. Remove the IAS so you can clean it's business end and the air passage. There's also a small air passage that comes up through the top of the throttle body on the driver's side that you can squirt. Don't spray the TPS with carb cleaner.