I just had spark plugs, ignition coil and oxygen sensor replaced 3 weeks ago. While out of town, I had a "service engine soon" light come on and it was misfiring badly. It happened out of the blue and I had to fix it or have it towed which would have been very expensive. A week ago I did put premium gas in it and it went away. I just filled up with regular again and it's pinging again. Before I had the coil, plugs and oxygen sensor replaced I could put regular gas in it without pinging? Any thoughts on why it is pinging now? Will I have to use premium gas from now on?