90 Accord EX.
While waiting for the carpool ride to come this morning, I was sitting in the car with the engine idling in park and heater on to stay warm.

The car ildled smooth at 750-800 rpm, but when I raised the rpm it would cut out at 1500 and drop to 1000 and repeat as long as I held my foot on the throttle at that 1500 rpm position. I did this 3 or 4 times and it would cut out as soon as the tach hit 1500.

Up until this morning, the car has run perfect.
I recently ( couple of months ago) changed plugs, cleaned EGR valve and EGR ports, checked/cleaned cap and rotor and did basic tune-up items to pass smog.

Any ideas on what to look for that may be causing this 500 rpm fluctuation.

 

Does it bounce or just drop?

 

It bounces up and down within 1 or 2 seconds. From 1500 to 1000 rpm.

Tried to duplicate the same condition this morning by holding the rpm at 1500 but it just remained steady.

 

Suggest cleaning throttle plate and bore around throttle plate, clean IACV movement.

Check PCV valve and hose are clear and functioning.

Make sure coolant level is good and not trapped air (check bleeder).

I suspect this happens when engine detects too high idle speed (air leak somewhere) and attempts to correct by reducing IACV air flow. Idle drops way below desired speed, IACV opens to increase speed, and cycle repeats.

Most older Accords seem to do this once in a while. I had a 90EX that did this when I accidentially left PCV disconnected after cleaning.

good luck