There could be a problem right there. You just had the emission problem fixed by them. Now the emission problem indicator is on intermittently, which, I assume, you did not have the problem before. There is no problem at all for you to drive the car, yet, you might have trouble to pass emission test next year. Some states in US just won't let you go as long as the light is on.
There are many reasons why the light is on. For example, the gas tank cap is not tight; leak in exhaust, etc. besides the other guy mentioned. If the light is on everyday the first time you drive, I kind of doubt if there was some "left over" in your system, more like some parts were heated up and sealed a leak in exhaust, etc.
Any comments, guys?
