Why does my rough idle not change if I disconnect or even swap two of my leads

I was silly and loaned my VS V6 Holden Commodore to someone. They decided to put 2 stroke fuel into it. It started running really rough almost straight away. When it was returned I was not told about the 2 stroke, as it was rough when I started it I straight away put injector cleaner and premium fuel in it thinking that it may have got some gunk in the lines. After a couple of days of it running roughly it decided not to run at all. I have replaced the fuel pump and filter, cleaned the tank out filled it up with more premium fuel and injector cleaner. I have changed the leads, spark plugs air filter, coil pack and TPS. After adjusting the throttle cable tension The car finally started again but idle really rough, and had to be started over and let idle for around 10 mins before the engine could be revved. When check again the spark plugs were completely black again, The have been change 3 times now. The car will drive but has no compression what so ever and when slowing down it will stall. It will go around 90kph tops and that is only in third gear sometimes if going down hill you can change into forth, never fifth gear. Even though there is plenty of spark going through the leads you can disconnect 2 leads leads, even swap them around and there is not even the slightest change in the idle. It seems no matter what I do The car just wants to run on 4 cylinders. Please help, what do I do?