[Excaliber]

OH, forgot, heres a BIG clue as it concerns octane and compression ratio. Engine 'run on', sometimes called 'deiseling'. There are several causes but the primary one is fuel octane to low for the engine.

You turn off the key and the engine continues to run, all though it runs poorly, it still runs, it won't shut off. This is very very hard on the motor, put it in gear and let out the clutch to STOP the engine from running.

Higher octane fuel (high enough for your compression ratio) prohibits this run on. If it still runs on with 93 octane perhaps your idle speed is to high or the octane really isn't high enough!

Mixed feeling on octane booster from me. Do bear this in mind. When it says it raises the octane by one point that is not from 92 to 93 octane. That my friend is from 92 to 92.1 octane. Not a big jump...