93 Buick Regal (3.1L) Stalls and poor gas milage!

[Harry-Florida]

I bought a 1993 Buick Regal (3.1L) a year ago and it has been running perfect until a month ago?, it only has 41,000 verified original miles.

The car started to run rough, and stall when I let the RPM go below 1000, and the gas consumption has been extremly high?

I replaced the plugs which were gapped very high (.60+) and fouled with soot. The car ran better but still not right! I replaced the O2 senser and the gas filter. The result was the car ran much better but it still stalls and the gas milage is better but still uses too much? I detect a little dark smoke from the exhaust and suspect it is running too rich? The OBD does not show any trouble codes and the engine service light doesn't go on except when it stalls.

With the price of gas and the danger of stalling in traffic I am at wits end! I would appreciate any thoughts on what I need to do next? Thanks in advance.