Typically, the rationale for why an intelligent designer is necessary in the first place apply equally to the designer.
If you're not saying that the intelligent designer is necessary, then a designer for the designer likely isn't either, however, why assume an unnecessary designer in the first place?
Sure there is. We are trying to explain the existence of a series of contingent beings. (A contingent being is one -- alive or inert -- that depends upon another being for its existence.) No contingent being can explain the whole chain. Therefore the contingent beings must all find their source in a noncontingent being.
Either that, or the chain doesn't work the way we think it does.
This doesn't get us to the Christian god, of course (philosophy never does), but it does get us to a being that is itself uncreated. This argument is as old at least as Plato and has never been really refuted (although I won't say there are no problems with it; there are, as there are with any philosophical argument/claim).
The argument is valid only as far as it says that, given the apparent rules of the universe we observe, it's impossible for a causal chain to be infinite, while at the same time, those rules require that causal events have causes themselves.
It doesn't get us to an uncontingent being, because by those same apparent rules, an uncontingent being is impossible as well.
This leads us to one of two conclusions:
- the apparent rules we observe don't work quite the way we think they do.
- the rules do work the way we think we do, but only within certain limits (e.g. after the Big Bang).
You must accept one or the other to allow for an uncontingent being, but when you accept either one, you undermine the original premises, and suddenly you can no longer say with certainty that all causal events must have causes, or that an infinite causal chain can't exist.
Why would not needing maintenance make the car better?
It was previously stated that a car that degrades, i.e. one that requires maintenance, would become less than perfect. However, the criteria for what makes something perfect are a bit of a side issue here.
The main point is that if a thing begins in a perfect form and then degrades, it is not as perfect as a thing that begins in a perfect form and remains in perfect form forever.