Backfires are generally an indication of a rich fuel mixture. Unburnt fuel go into exhaust and either the heat of the catalytic cnoverter or manifold ignites the excess fuel.
Some causes of this can be; vacuum leaks, airflow sensors, O2 sensors are often the issue especially on your year vehicle. You could also have an exhaust leak near the O2 sensor which is making it think the air/fuel ratio is lean and it will dump tons of fuel into the engine in that situation. Failed fuel injectors or fuel management is the bottom line for tracking down this problem.
So, check for vacuum leaks and exhaust leaks.
I would get the trouble codes from an OBD tester before you do anything else. Any qualified repair shop can do this for around a half hour of labor.

Answered by DrCranknWrench (expert)
3,292 answers provided

So is the car okay to drive or does it need to sit until the sensor can be changed out

Response from Chavas20
1 question asked

When problems occurs, it is best to get it resolved asap.

misfiring can cause the catalytic converter to glow red hot when engine is running and can aggravate the problem and cause other damages.

If you are into DIY, try the link.

http://www.2carpros.com/articles/mitsubishi-trouble-code-definitions-and-retrieval-procedure-for-odb1-system

Answered by KHLow2008 (expert)
39,956 answers provided