My 2004 honda accord 2.0l i-vtec car vibrates badly when i switch on the AC and the car is idle but stops when i accelerate. Start to vibrate again when idle without me applying any acceleration.
Sounds like the IAC unit is not operating for some reason, the ECM controls engine idle and usually bumps the idles speed up when a load like A/C is turned on, so it could be a few things, the ECM may not be getting the A/C signal, or the IAC unit itself is bad or plugged up, or even a wiring problem, a "live data" scanner would be a great help with this as then you could see if the ECM is getting an A/C on signal, about the only thing you can do without any equipment is make sure the throttle body is clean and if you have some knowledge you can remove and clean the ISC unit and the passages. HTH
Could be the idle air control as stated above and it could be many other things, you need to take your car in for a professional check. Without the diagnostics, you're shooting in the dark. Cars today are much more complicated, unless you are a professional, it's hard to know.