Surging while idling

my 1988 22RE Fuel injected seems to be surging in RPM's when idling ... not a constant thing but occurs at random times quite often. Oxygen Sensor?

 

It can be a number of things but I'd start at the throttle body first. Make sure it's clean and that the throttle plate is closing fully as well as cleaning the IACV. Then work on finding any vacuum leaks.

 

Two questions that may help...
First, is the idle above 1000 RPM by much at all? Say 1100 or higher?
Second, is the surging happening when the brakes are pressed, even just enough to turn the brake lights on?

The ECU has a little program Toyota thought would be a good way to save us some fuel by turning the injectors off when we are braking to a stop. If the RPM are above 1000, roughly, and the brakes are pressed, you must be slowing to a stop. In their minds.
Well, if the rpm are set too high at idle, the program kicks in, the injectors shut off until the idle drops low enough to be considered at idle, so it turns the injectors back on. Then the rpms rise above the limit, the program kicks on, shuts the injectors off until the rpms drop, etc, etc.
I believe it uses the idle switch on the TPS that tells the ECU is at idle, and the brake light switch on the brake pedal to determine if you're "stopping". And, of course, the engine RPM reading.

Just offering a possibility.
Pat☺