Our Shia faith in Quran is: Quran is absolutely intact and saved by Allah The Glorious from any change, distortion or alteration. Narrations which suggest change or distortion in Quran are mainly in Sunni books including narrations from Umar Ibn Al-Khattab who claimed that Sura Al-Ahzab used to be as long as Sura al-Baqara. (al-Soyooto, Al-Dorr al-Manthour 3:208) and Ayisha who claimed that a Sura was eaten by a pet (Sunan Ibn Maajah 1:625).
Few narrations in this regard came from Sunni books to some of our Shia books but our leading scholars were and are always very clear in rejecting any claim against the fact that Quran is intact. Some narrations in our books might mean that people distorted the meaning (Tafseer) of some verses away from the real meaning explained by the Prophet (SAWA) and his Ahlul Bayt (AS) which is a sad fact, but it never means that Quranic text was distorted by any way.
Leading Shia scholars al-Shaikh Al-Saqouq (381 H), al- Shaikh al-Mofeed (413 H), al-Sayyed al-Mortadha (436H), al-Shaikh al-Toosi (460 H), al-Shaikh al-Tabrasi (548H), al-Shaikh al-Bahaa'ee, al-Faydh al-Kashaani, al-Shaikh Kashif al-Ghitaa', al-Sayyed Sharaf al-Deen, Allamah Tabataba'ee, al-Sayyed al-Kho'ee, al-Sayed al-Khomaini, al-Sayyed al-Gulpaygani, al-Sayyed al-Borojordi, al-Shaykh al-Saafi, al-Sayyed al-Sistani, al-Sayyed al-Hakeem and all our leading scholars are very clear in confirming the fact that Quran is absolutely intact from any change or distortion.