1998 honda accord , 4 cylinder , 199,000 miles on it. The oil looks black. Car is idling rough . Hooked up for Dia. check and it read misfire on all 4 cylinders.
Misfires happen for many reasons. All four cylinders usually means problems with the coil, distributor, coil wire, spark plugs, or ignition module if the problem is in the ignition system. If the ignition system is OK, then start looking at maybe a compression problem. Oil in radiator might also mean a blown head gasket.
UPDATE: This is a duplicate post with additional info. Please use your original post, and reply to it.