Oil drops about a quart

Engine Mechanical problem 4 cyl Front Wheel Drive Automatic 134000 miles

I just bought a 94 cavalier. The car drives fine, doesn't overheat, shifts great, but it idles rough, it runs rough and it's only getting about 26 MPG highway driving only. It does not appear to leak anything, but the oil drops about a quart in and a half in 3000 miles, and the coolant seems to disappear into thin air. I clean out the upper intake manifold, cleaned the 02 sensor, put new plugs wires and an air filter in as well as put fuel system cleaner into the gas tank. These things helped the idle. The intake was coated with this black crap which I assume is from the exhaust. Also when I did my last oil change the oil smelt like gasoline or exhaust (it was hart to tell). Also the car smells like burnt and un-burnt coolant after being driven for half an hour. Any clue what the issue is.