Is there iniquity in my tongue? - This is a solemn appeal to their consciences, and their own deep conviction that he was sincere. Iniquity in the tongue means falsehood, deceit, hypocrisy - that which would be expressed by the tongue.
Cannot my taste discern perverse things? - Margin, palate. The word used here חך chêk means properly the palate, together with the corresponding lower part of the mouth, the inside mouth. Gesenius. Hence, it means the organ of taste, residing in the mouth. The meaning is, that Job was qualified to discern what was true or false, sincere or hypocritical, just or unjust, in the same manner as the palate is fitted to discern the qualities of objects, whether bitter or sweet, pleasant or unpleasant, wholesome or unwholesome. His object is to invite attention to what he had to state on the subject. To this proposed vindication he proceeds in the following chapter, showing the greatness of his calamity, and his right, as he supposes, to complain. Their attention was gained. They did not refuse to listen to him, and he proceeds to a fuller statement of his calamity, and of the reasons why he had allowed himself to use the language of complaint. They listened without interruption until he was done, and then replied in tones of deeper severity still.

Is there iniquity in my tongue? - Am I not an honest man? and if in my haste my tongue had uttered falsity, would not my conscience discern it? and do you think that such a man as your friend is would defend what he knew to be wrong?
I Have done what I could to make this chapter plain, to preserve the connection, and show the dependence of the several parts on each other; without which many of the sayings would have been very obscure. The whole chapter is an inimitable apology for what he had uttered, and a defense of his conduct. This might have ended the controversy, had not his friends been determined to bring him in guilty. They had prejudged his cause, and assumed a certain position, from which they were determined not to be driven.

Is there iniquity in my tongue?.... Meaning in his words; either those which he uttered when he cursed the day on which he was born, or in charging his friends with unkindness and falsehood; otherwise the tongue is a world of iniquity, and the best of men are apt to offend both God and men in word:
cannot my taste discern perverse things? which is to be understood not of his natural taste, which very probably through his disease might be greatly vitiated, and incapable of relishing his food as in time of health, and of distinguishing good from bad; but of his intellectual taste, or of his sense and reason, his rational and spiritual taste; he had his senses exercised to discern good and evil; he could distinguish between right and wrong that was said or done, either by himself or others; be had the use of his rational powers and faculties, and therefore not to be treated as a mad or distracted man, but as one capable of carrying on a conversation, of opening his true case, and defending himself; see Job 12:11.

Will you say that my guilt lies in the organ of speech, and will you call it to account? or, Is it that my taste (palate) or discernment is not capable to form a judgment of perverse things? Is it thus you will explain the fact of my having no consciousness of guilt? [UMBREIT].

Is there - Consider if there be any untruth or iniquity in what I have already said, or shall farther speak. Taste - My judgment, which judgeth of words and actions, as the palate doth of meats.