Then yes they are immoral. I am myself, agnostic, but can't bring myself to belief an objective morality based on a book a few thousand year old. Perhaps it's true, perhaps it's not. But I need better reasons than what I'm exposed to now. If morality is subjective then the question is wrong.
Morality is not dictated by one's religious beliefs or lack of religious beliefs. And agnostic is someone who questions things and looks more deeply into things, one who does not just accept things on faith or on face value. It is good to question things and look more deeply into them. Therefore, agnosticism is not a question of morality; it is only a matter of someone who wishes to explore more deeply and gain more insight into questions of religion and religious beliefs.
As a history professor once told me, religion is simply a natural instinct in humans to use the supernatural to explain events that they can not. Agnostics are not immoral, but simply focus on their lives, and focus on living that life how they want, so that they will die happy.
Agnostics are not immoral. Or, rather, agnostics are not more or less immoral than the general population around them. Morality does not inherently come from religion or from God, but is of a more personal origin, and is created around society and populations rather than through some divine source of inspiration.
Agnosticism is the view that the truth values of certain claims—especially claims about the existence or non-existence of any deity, as well as other religious and metaphysical claims—are unknown or unknowable (Wikipedia). I do not believe agnostics are immoral and assuming they are is quite immoral in my opinion. These people uphold what they believe to be true based on their experience, there's nothing wrong with that.
An agnostic is one who does not know if the claim can be proven, that's it.
You can still not know by evidence and still be a theist, the question of knowledge does not equal your personal belief.
This is why we have Agnostic Atheism, Gnostic Theism, Gnostic Atheism and Agnostic Theism.
You do realist that don't you? Morality is a very man made concept. What is right and what is wrong. That is morality and what is right to you, you can always find someone who thinks that it is wrong. So who is the right and wrong? Answer? None.
It's a matter of perspective. Might as well ask are non vegetarians immoral. As according to vegetarians, meat eats are immoral for killing another life. That is just one example to mention. There is countless list of contradicting believes on morality. So no. Agnostics and even so biased being an agnostic myself. We are not immoral.
There is no such thing as immorality just as there is no such thing as morality. It's called perspective.
No, agnostics are not inherently immoral, any more than an atheist or a Christian is immoral. A person is not immoral simply because they do not believe in God, or that they do not believe that God is active in the world and loving. Agnostics can have ethical standards and live by them, just as Christians or atheists can.