1996 Cadillac Deville engine mis-fire?

Things I should mention:
1st time Caddy owner of a 96 deville with 150k miles. Have owned it for about a month. So far, it has shown consistent rpms both idle and running. Coolant temp stays between 206 and 212. Havent had any problems until today. After washing my engine with a common degreaser and a gentle spray down with a pressure washer (making sure not to touch the coil system) I started the car and it felt like it was choking. After running a diagnostic, the computer read "troubleshooting PO300". I noticed white fumes from the engine. I know this could be leftover degreaser burning off but I also feel that one or more cylinders may be mis-firing. How can I troublesoot this without paying hundreds of dollars or taking it to a mechanic? Please help. I spent all my money to buy the car and am broke until next payday.