Yesterday, I was leaving work and got in the car. Started the engine and I got warning sign says, "Tighten the fuel cap". So I did tighten the fuel cap right away, still the warning was on during all the way to home. This morning I started the car and no more warning sign was there. What's up with that??!!

 

I am guessing this is a evaporative emissions system warning caused by a loose fuel cap.

The manual has several conditions (see p 299 in the 06 manual), and this description sounds as if it might best apply to yours:

The CHECK FUEL CAP message,
displayed after you turn the ignition
switch to the ON (II) position or
start the engine, should go off after
tightening the fuel cap, turning the
ignition switch off and on, then
driving over 12 mph (US) or 20
km/h (Canada) for at least 10
minutes. Due to different driving
conditions, itmay take a few drive
trips to make the message go off.

 

if it were just a normal car, your CEL would come on, at least Acura is smart enough to differentiate between the two!

 

Some cars will just run like crap. You take it in to the dealer and they tell you the cap was loose or off.