I just bought a 1990 Honda Civic standard hatchback with the 1.5L and a manual 4 spd. (no AC or power windows, etc.) and FI. When warmed up, the engine idle stays high for a period (i.e. 5-10 seconds) and then starts oscillating on a regular pulse from probably about 1500rpm to 700rpm (I estimate a 1-2 second oscillation period). The car runs fine, except for this oscillation, which is keeping me from getting the car smog tested. Any ideas what it could be?

. Remove electrical connector and both bolts (12 mm) securing the Idle Air Control Valve (IACV) to the plenum. Also, remove both hoses going to the IACV. Clean the IACV and hoses with a spray can of brake cleaner--be sure to wear safety goggles.

. Remove air duct going to the throttle body. Ensure upper and lower throttle body ports are clean. Dirt tends to build-up around the top port.