Do a leak down and post the tesults of each cylender that will tell you if its valve seals or rings, also is it leaking any water, and whats the exhaust look like? And when you take the spark plugs out for the leak down, replace them with NGK and see if it helps anything. If it is a valve seal, dont drive the car untill you fix it, or you will burn up the valve seat, and then you need to take it to a machine shop (been there done that)...