Reaction of Diols with HX hydrohalic acids, Competing SN2 Reactions
Bob:
Here is the likely process. The alcohol 1 is protonated to provide intermediate 2 which undergoes SN2 displacement. The closure of 3 to  tetrahydropyran 6 is unlikely under the reaction conditions. Rather a second displacement via 4 would lead to diiodide 5. If the tetrahydropyran did form, ethers are cleaved by HI. The conversion of 3 to 6 is normally accomplished in the presence of base (NaH/THF).