Rough idle, Smoke from exhaust!

Hello all, when it rains it pours! 1990 Cherokee Pioneer, IL6 4.0L 5 Spd. Ive been dealing with an overheating issue for two months now, I have been "burping" air from the temp sender after it cools every night for a week or so. Still over heating, anyways now, I went out this morning to start it so I could test drive it AGAIN to see if it still overheats. I started it and immediately it was running like crap, rough idle, smoke from the exhaust and a hissing sound , kinda like a vacuum leak from the rear/top drivers side of the engine. This is a first, it always runs and idles great! I looked at the rotor and distributor cap, it all appears to be in descent shape. I haven't changed the plugs since Ive owned it , about 3 months now. Any help/suggestions is always appreciated.

Hissing? Look for a vacuum leak. You would do well to test vacuum anyway, to see how it's behaving.

If it smooths out and the smoke clears after a while, it might be a dribbling injector. But I'd check the vacuum anyway. If you buy a new vacuum gauge, it will usually come with a little diagnostic chart, which is very handy.

knd of sounds like it could also be head trouble, like bad gasket, you kno cuz its over heating and burping...... the hissing could be unrelated.... worst case scenario, i would check them both though, but overheating, rough idle, and burping, sounds like a head issue.

Thanks again, I will let you all know what I figure out!

I removed the exhaust/intake manifold and installed a new gasket. What a pain in the A*S! Anyways, I replaced the water pump while I was in there to try and rule out another part that could be causing my overheating issue. It took me about 9 hours by myself. I turned the key and SHIZZAM! It is running and idling great again with no smoke from the exhaust! What a relief. As far as the overheating issue goes, I have replaced the thermostat, thermostat housing, water pump, coolant bottle and cap with the volvo cap, the upper and lower radiator hoses and flushed the radiator. The clutch fan is good, I will replace the radiator ASAP if I can find the right one. It appears that the 90 Cherokee Pioneer XJ came stock with a one core radiator. Not sure why I couldn't just install a one core but it seems highly recommended that I install a 2 core.