I have an Olds 88 the engine is running rough, it did this a couple months ago, change of the coil pack and all was fixed. But not so lucky this time, coil pack, plugs, and wires have been changed. The oil dipstick has a hint of gas smell (I'm assuming from not all the gas being used while firing) Service engine soon light did come on but the only code was 44 oxygen sensor lean O2. Any ideas??? I have read other posts and will look into replacing the MAP sensor and IAC.

clean the maf, check for vacuum/air leaks. you can run the engine spray with carb cleaner and listen for changes in pitch

L27 are prone to burn exhaust valves. Do a compression check. Mine sounded like a bad rocker arm at idle.