Q. Is saying Im Irtzeh Hashem (If Hashem wills) when asked to perform a mitzva such as attending a shiur or a minyan similar to saying Beli Neder or without promising?
A. It would seem to depend on how it is said and with what implied intention.
However, Horav Shlomo Miller’s Shlit’a opinion is that one should say Beli Neder even when saying Iy”H..
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a.