In essence the Kalam cosmological argument boils down to the following tenants.
1) Everything that has a beginning of its existence has a cause of its existence;
2) The universe has a beginning of its existence;
3) Therefore the universe has a cause of its existence and this cause is god.
You may hear this argument in many forms but they all boil down to these three tenants, remember theists have no original arguments so they just repackage the stuff that doesn't work and hope no one will realise.
All these premises I would have no problem with (except the god part), and now let me explain why with 2 simple reasons.
If we accept that the cause is god then either this god is part of reality or not part of reality.
1) If we accept that god is not part of reality. Then the cause can be pointed towards the singularity that started the Big Bang. Or in a recent theory the cause can be pointed towards the collapse of a 4 dimensional star which created our 3 dimensional universe. Either way we are just calling god a starting point, and then god is meaningless and we may as call god a singularity. So this argument all comes down to the definition of a word, and we know theists love their words games.
However theists are not using argument 1, they are referring to a god that is a creator and sets rules for us (these rules are in our reality, so go exists in our reality).
2) So, if we accept that god is part of reality. Then god exists in this reality and can be tested for. Or god exists outside of the universe however can still effect our reality and as such can be tested. Either way at this point we can test god. Let me note here that every test I know for god fails.
So either god according to the cosmological argument exists in our reality and can be tested or god does not exist in our reality and is useless. So what's your god?
If you have a lot of time and patience, here is a fantastic debate between William Lane Craig and Christopher Hitchens. In this debate the Kalam cosmological argument is discussed.