Will do/check your suggestions.

Well the check engine light is still turning on for a few seconds once in a while.

Last night I reved the engine at 5,000+ RPM. It seems that this technique does not work.

Another observation that this happends kapag naka 10Km or more na ang naitakbo ko from a cold start in the morning.

BTW, I am using caltex silver unleaded and is gassing up on the same gas station for about 2 months now. (loyal ba?)