Most likely the problem is that your IAC needs to be cleaned. At least I always recommend cleaning it before replacing it. Most of the time that's all that is needed to repair a problem like this. You should also check your air cleaner element if you still have the "lifetime" air cleaner. If you haven't done a tune-up in a long time, then you should see about that also. The spark plug boots are replaceable- as well as the spring that connects the coil to the plug, it comes with a new boot.