The other day I was out, parked, came back, started the car and it ran rough for a little while and the "service engine soon" light stayed on! I shut it off, started it again, and it was back to normal and has been good ever since. The only thing that I can think of might be the spark plugs because for a while my dad ran low octane in it and maybe detonation damaged them a little? I don't suspect anything else because it has 25,200 miles on it only. (1991 4.9) I do notice a little shake at idle until it is fully warmed up. But then if it is the plugs, wouldn't it always run rough until I change them, or could fouling be the culprit? Any ideas? Are Bosch platinum 1's ok in these engines? I don't want anything too fancy in the way of plugs because Iridium's are 20 dollars for a pair here! And Bosch 4's are 15 dollars for a pair, too expensive. I do want a longer lasting plug because of the awkward location of them on these sideways engines.