If you have a poor ground connection the car will not run right, if at all. It just depends on how tight it is, and if it stays that way without the bolt/nut.
A recommendation if you choose to follow it and you want a DIY:
Get a small steel hose clamp around it and tighten until you close the gap. It should do the job. It is no way a substitute for a proper repair... but it would work.