1996 monte ls, rough idle/back fire

i have a 96 monte ls and it is idling kinda rough...not bad but bad enough to notice. While running it has a kind of burning smell coming out of the exhaustbut its not a gas smell. It also backfires when i give it a hard rev and let off i thought that it was the exhaust tip that i had put on it but i took it off and it still does it...could it be the spark plugs since im running cheap bosch platinums or the o2 sensor causing my cat to burn out hence the smell?...Also the metal tube thats comes out of the thermostat housing and goes to the heater core is leaking around the quick connect...any ideas on how to fix it

Dorman makes that quick connect (part number 800-401) or you can eliminate it and put a hose nipple and a new piece of hose. Look along the seam between the intake manifold and the heads/block. If you see any signs of seepage, you most likey have an intake manifold gasket leak that may be causing both the funny smell from the exhaust (coolant is getting in the engine) and the rough idle/backfire (due to a vacuum leak). Intake gaskets are a VERY common problem on 3100 V-6's. Get rid of those JUNK Bosch plugs and buy either AC-Delco or Autolite platinums. It may be time for plug wires too.