stalling / surging idle

Last evening, I was driving my 97 Cav across a parking lot at very light part throttle. Lately, when driving at very light part throttle, the engine will slowly lose RPM's and stall or become very sluggish. When I stopped the car, the engine started surging wildly between 500 - 1200 RPM's. I was waiting for it to either smooth out or die. It just kept surging for about 15 seconds before I revved the motor. I held it at 3,000 RPM before backing off the throttle. It then took probably 10 seconds to slowly return to 600 RPM idle. Afterward, I looked for a check engine light - none! How can a car run so rotten and not throw any codes? Apparently, the computer thinks all is well.
I'm puzzled?
Any thoughts will be appreciated.
Thanks,

Clean the throttle body, and remove the IAC motor and clean it and the passage it goes into.