Running rough

My wife's car, a 2003 Honda Odyssey. She says there has been no problems with it. 3 days ago she drove it home from the high school (less than 1/4 mile from home) and said that it was running rough and smelled like it was burning. Of course she told me when I was running out the door for work (I work 48 hours at a time). I check the oil level and it would not register on the dipstick. I put 2 quarts of oil in and it did not even touch the bottom indicator (lowest hole) on the dipstick. The van remained unmoved until this morning when I got home. I performed an oil change with filter, air filter and park plug change. Now no burning smell but car is still idling and running rough. Emissions indicator flashes when accelerating but is on constant when not accelerating. The Traction Control indicator is also on.

Any ideas? If I take it to a dealer, it's $126.00 just for the diagnostic. Being a firefighter, I need to be frugal with money. Thanks