I would suggest replacing the resistor first. I removed the resistor from my '88 260e and at first I thought it performed a little better but after a week or two, I noticed that it misfired slightly when idling, something it had never done before. It also was bogging down when driven with a cold engine. I replaced the resistor and it's back to normal.
I don't think my problem was gasoline related because I always use 91 octane from the same station.