I had a CEL code 046 and failed emission test. I got my o2 sensor replaced. The emission test is reasonably good (passed well-below threshold) and CEL went away for 1 day only. Now CEL is back on.

This time the code is 92 "Evaporative Emission Control System insufficient purge flow". The strange thing is car has passed the emission test two days ago..

Is there a critical impact of this system to the health of the engine (or the car in general)?

Any suggestions? what is the first place to look? fuel cap?