Problem: Honda idle air control system issues can cause erratic or bouncing idle speed, poor fuel mileage, a check engine light, and engine stalling. The most likely cause is a dirty or failed idle air control valve (IACV), but leaking vacuum lines, failed intake manifold gasket, leaking throttle body gasket, and leaking or failed IACV valve should also be investigated.
Repair: Check engine light diagnosis and testing; idle air control valve (IACV) replacement; throttle body cleaning.