My car usually idles at 750rpm but for the past 2 weeks I've been noticing that the idle has gone up to around 850-900rpm. In the past it would only go up to that level when I have the A/C on. The rpm would sometimes drop back to 750 when I hear that clunk sound just like the sound the car makes every now and then when the A/C is on. I also noticed that last week the car vibrated when I was at a stop with the rpm at 750. But if I give it some gas to move the rpm up just a little to around 900 the vibration goes away. This only happens for about the first 5-10mins of driving from a cold start in the morning. The weird thing here is that I don't feel the vibration during the 3-4mins that I let the car warm up in the garage. The weather in the morning here is not that cold either, around mid 50s. BTW the vibration is enough to make a rattling noise from the right side door.

 

As for the vibration I would chk all the motor mounts ,, especially the rear one.
As for the idle going up a bit you might want to make sure that the throttle plate closes fully,, and also clean it ,,

 

Ok I'll check the motor mount again. I just check all of them after I replaced the front one because it was cracked 2 months ago. But won't a broken rear motor mount cause the vibration all the time? The car only vibrates when I'm stopped for the first 5-10mins of driving. Theres no vibration during the first 3-4mins when I let the car warm up in the garage either.

 

when you let the car warm up in the garage i would have to assume that it is in park or neutral,,
when you are stopped at a light, i would have to assume that car is in gear ( you got A/T tranny ) thus more load on the engine and on the mounts ..A/c on as well ??? if so , even more load applied to the engine ..
Also whem first starting the car up in the morning ( engine cold ) the idle speed is usually a bit higher til engine is warmed up ,, the higher the idle the less the vibration ,,

 

Well I let it warm up till the rpm drops to idle speed before I take off so I guess you're right about me not feeling it because it's in park. I'm just puzzled with why the vibration goes away after a while and only happens on my first drive of the day. I usually take the car out 2-3 hours after and the vibration isn't there. Also I started using the A/C again today. Turned it on at a red light and saw my rpm drop from that 850-900 range straight down to what the idle should be at 750rpm.