The sparkplugs were replaced maybe 2 months ago. According to the mechanics, there were no adjustments needed since it is an EFI and the computer will always reset it to its original setting. Is this accurate? What should I do? As with my high idle problem, if I don't experience it after the cold start, the car runs smoothly throughout the day. (Probably since the engine is already hot?)

I was observing it a while ago after a few minutes of driving from cold start, every time I changed gear (full clutch), the rev goes up without touching the accelerator. But after driving for several minutes, everything was already normal. I did not experience the high RPM problem that I had yesterday. I recently had may oil changed using 20W-50 mineral, I used to use a 20W-50 synthetic blend oil. Could this be causing the issue?

Hope you can further help me out. Thanks CivicVTi.