my engine misfires when I first start driving but as soon as it "warms up" (it's summer) it runs smoothly. The diagnostic reads random misfiring. The first mechanic replaced all the cylinder coils, it came back after a week, the second mechanic said it was a loose spark plug, and it ran smoothly for 4 days then started misfiring again. It doesn't shake like others have described and it doesn't backfire, I just don't get any juice when I first start out, but then it runs smoothly. Any ideas?