How to fix a check engine light with code P0302? And Pass Oregon DEQ? on 1997 Mercury Sable

I check the code it pops up P0302, misfire on cylinder 2. I had Spark plugs check and coil changed. After code still pops up. I had a shop do a test to find out what the cause is and was told to check with Ford Dealer. I have good combustion, air flow, gas, ignition. They couldn't find out. I did not take it to the Dealer for the ridiculous price to diagnose. When to a second shop said the same thing. When I had the tune-up the car didnt bring the code up till miles later then recently code P0302 and P0303 code pops up. Reset the computer the only code after 5 miles pops up is P0302. I cant pass the DEQ with the check engine light on.

by in Gresham, OR on April 13, 2013
2 answers 2 comments
ANSWER by on April 14, 2013
you have a misfire in cylinder 2 and 3 recheck pluges and wires
COMMENT by on April 14, 2013
I checked that still persistent. Cylinder 3 had rusted and blown spark plug. Can 02 sensor cause misfires.
COMMENT by on April 15, 2013
no o2 sensor wont make any difference
ANSWER by on April 15, 2013
Hello dear costumer the cause of misfire since you check all the thing you mention injector or burn valve or bad valve spring or damage head gasket between # 2 and 3 and get coolant in the compestion champer or bad TPS