Higher octane fuel does nothing for you - especially if you aren't tuned for it. You can skip that.
A cough / sputter could have been anything from a little water in the gas to a missed spark.
I'd start by pulling out the spark plugs and checking them for wear.
Also check to make sure your airfilter is clean.
Originally Posted by robb15033
-Always replace the fuel filter every oil change or every other, depending on type of oil used and recommended intervals of change. (Twice a year maybe).
You HAVE TO replace the ignition parts now as a good start to a preventive maintenance program & help eliminate or second guess yourself. Copper spark plugs at the very least. Plugs, wires and ignition coil at the most.
-Check for vacuum/air leaks around upper intake and around engine bay.
-With everything checked out and good to go, give it a Seafoam treatment. One can in the gas tank, more importantly, one can sucked up into engine while running through any vacuum line or straight through pcv valve.
1998 Roush: M112'd Aluminum block 4.6L 2V 6 speed track car
1999 SVT: Mostly stockish
1970 Mach 1: Resto-modded monster
2000 Roush #5004 - World's FIRST M112'd V6 Mustang. Sold, but not forgotten.