Exhaust leak and crappy gas mileage/rich mix

[LonelyDrifter]

So I found out that the right-hand side of my exhaust manifold had 0 of 4 bolts connecting to the head. All four on the left. Im pretty sure my exhaust leak (ive smelled it now for awhile with my windows down) is coming around this unbolted section and am going to take the manifold off, replace gasket, and put back together (which would be a miracle).

Ive been getting about 160 miles/tank for gas mileage recently, and today, when i actually noticed the black smoke wafting through the blackened, boltless holes on the manifold, my car was wanting to kill at low rpms and idle. My plugs are BLACK, as is my O2 sensor, all of which Im replacing.

Does anyone think that these are related (I wasnt throwing any codes, which makes me think that the O2 thought it was ok and needed to run richer with the leak before it in the system...) Anything else I need to check?

Other thoughts?

[180fan]

probably your coolant temp sensor or your mafs. The soot covering your plugs will also end up on your o2 sensor. You might also want to check the resistance across the injectors and the vac across the fpr.

[LonelyDrifter]

Would either of those throw a computer code though? Thats what Im most confused about...

[LonelyDrifter]

Thanks for the response, by the way. Anything helps. The only thing I know about cars is what I've had to fix out of necessity. Which now includes fuel injectors, alternator, starter, front struts, master cylinder, etc. Ha : )