Toyota Repair: 2003 Echo - malfunction indicator lamp on!, emission control system, 2003 toyota echo

Question
Hi Ted,
about a week ago a malfunction light turned on in my 2003 Toyota Echo (mileage 42.000). Thanks to this webpage, I knew I can turn for help to Autozone (big THANKS!). To my surprise I got four different troublecode readouts:
- P0304 (misfire in cylinder #4)
- P0441 (purge flow in the evaporative emission system is incorrect)
- P0442 (a small leak exist in the evaporative emission control system)
- P0446 (a malfuntion in the electrical circuit for the vent control in the evaporative emission control system).
My car was properly serviced every 3-4000 miles mostly at Toyota dealer's and that is the first major problem. I can only remeber one ignored service advice - I did not change AC filter about 6 months ago as it seemed too early. Could it be the cause of problems? Is it safe to drive the car right now? What repairs would you suggest? Would you please estimate roughly the costs?
Thanks a lot for your help!

Answer
The first code is obvious there is an engine misfire that needs to be addressed in the #4 cylinder.
The rest of the codes are emission control related and do not affect driveability, all of these codes normally indicate a leaking gas cap or a gas cap that was left loose or a missing gas cap.
The emission control malfunctions are still covered under the factory emission control warranty(3yr/50,000miles)so I suggest having the dealer check it out, the misfire may or may not be covered, depending on what the problem is, I highly recommend taking it into the dealer, you may have it all fixed at no charge. Let me know what the diagnosis is that the dealer presents to you and their recommendations and I'll add my comments.