My '88 gt smokes really bad white smoke. It squeals a little bit from the belts when it is first started cold. There was nothing in the oil when I changed it. The engine doesn't idle smoothly and jerks every now and then. I changed the oil, oil filter, air filter, and pcv valve and I cleaned out the IAC. The problem is still there except the car doesn't lack any power. There is also a hissing noise coming from behind the engine and by the side of the radiator after the engine is turned off. What do I check or replace next???