i have a 2000 honda accord lx. 2.3 liter engine with the vtec 5 speed manual transmission. when it is first warming up, it idles at about 1500 rpm and is completely fine. once it warms up, the idle drops to around 700 rpm and a vibration starts in the steering wheel. it almost seems as though the engine is idling too low. there is no check engine light or anything like that either. what is the normal idle speed and if it is low, what do you think could be the cause(s)?