I ha e a 99 s80 2.9 and my brother in-law put about 2 gallons of mixed gas in my car. The next day it started running super rough and I immediately went over and put good gas in and it took about most of the day for it to start running a little better but now it has no power. I added some fuel injector cleaner but it did no good when I put it in gear it acts like it has no power whatsoever. Any help would be appreciated

 

you have oil in your gas which is going to foul your plugs and make the car run rich which will mess with the O2 sensor's feedback. You can start by cleaning or replacing the plugs but the best solution is to drain the tank and refill with fresh gas. I suppose you can save the old gas for your brother-in-law's chain saw or back pack blower :-)