Problem - my idle oscillates mildly after it is through warming up. RPMs will swing between 600 and 800 every couple of seconds while idling. The vehicle performs fine during the warm up period when the choke is on, and also when the throttle is open. I just had the idle control valve replaced (dealer said it was broke) and it helped alittle. I took a trip and got 18-22 mpg which is right. It starts rough, as if no gas, coughs alittle as it is starting, will quit if I don't goose the pedal, then it will smooth right out. There are 235,000 on her. I had the upper end, including valve guides, rebuilt at 225,000 and compression is fine and the plugs are carbon free. The O2 sensor is fine.
What is making the idle oscillate? Injectors? Vacumn leak? Air in the antifreeze? Fuel distributor?

If someone has suggestions, I could use some right now.
Thank you, Dave