Lower octane fuel would not cause the indications the OP listed.

 

My car sat for five months. Now that it has been repaired I am trying to get it to run. I added dry gas to the tank a month ago. Car idled for 45 minutes just fine. Drove about two miles then it started spitting black smoke , cutting off & won't hold idle. SESL code P0506 9( idel related) lights up. I'm thinking it may be the gas. I replaced the crank sensor thinking that might be the cause but no luck. Could it be the gas??

 

ok went to on the run and fill up with some 93 octane and added Lucas octane booster. I could feel the differenceoff the bat! However, I still get a little bogging. Possibly the ECU has to reprogram itself. Anyways, I have an appointment at the dealer I bought it from. Trans makes a rattleing noise when clutch isnt depressed or when car is in neutral. seems like a throw out bearing. i may be thinking that the throw out bearing isnt letting the clutch become disengaged all the way and in reason giving me this issue.