weird idle

I have a 1990 accord coupe with no modifications. When I stop at a light or anywhere for that matter, the engine speed comes down very low. Sometimes down to 300rpm. After a few seconds, the idle comes back up to normal 750 rpm. This happens every time I lift my foot of the accelerator and let the rpm's drop. My car is manual.

I cleaned out the egr passage in the intake manifold but the problem is still there.

Any thoughts on this subject would be appreciated.