That verse from Timothy always comes up. How many centuries more will it take for sola scriptura advocates to understand the difference between "all" and "only."
2 Timothy 3:16-17
All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness; so that the man of God may be adequate, equipped for every good work.
The Scripture (OT and Apostles' teachings, see post #45) is sufficient for man of God.
Furthermore,
1 Timothy 6:3-5
If anyone advocates a different doctrine and does not agree with sound words, those of our Lord Jesus Christ, and with the doctrine conforming to godliness, he is conceited and understands nothing; but he has a morbid interest in controversial questions and disputes about words, out of which arise envy, strife, abusive language, evil suspicions, and constant friction between men of depraved mind and deprived of the truth, who suppose that godliness is a means of gain.
Teachings that vary from Scripture are not permitted by Paul, and show that the person teaching those doctrines understands nothing.
Therefore, Scripture is sufficient for the man of God, and teachings that vary from Scripture show a lack of understanding.
So, if someone is teaching, it must be compared against a standard, which is the Scripture, just as the Bereans did with Paul:
Act 17:10-11
The brethren immediately sent Paul and Silas away by night to Berea, and when they arrived, they went into the synagogue of the Jews.
Now these were more noble-minded than those in Thessalonica, for they received the word with great eagerness, examining the Scriptures daily to see whether these things were so.
Likewise, Jesus showed to the travelers on the road to Emmaus:
Luke 24:26-27
"Was it not necessary for the Christ to suffer these things and to enter into His glory?"
Then beginning with Moses and with all the prophets, He explained to them the things concerning Himself in all the Scriptures.