When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Could it be that the coil that was replaced was shot and ANY coil would have made the car run smoother. Coils, to me, never wore out -- they run good till they BLOW out. A connection could have been bad or the dialectric grease gone causing the old coil to overheat. When the new coil was put in, new grease would have also been applied.
The only thing we seem to need to worry about is the spark plug wires loosing the juice on the way to the gap. Often overlooked and a pain, I'm a big believer in replacing them every few years or so depending on the climate where the car is driven the most. This is one sure guarantee to get a smooth ride.