Solubilities in the system comprising acetonitrile (1) and potassium iodide (2) have been reported in three publications over a very limited range of temperatures. No data appear to have been reported for the solubility of (1) in (2). Walden1 determined solubility of potassium iodide in acetonitrile at 273 K and 298 K by an analytical method. Varlamova et al.2 carried out measurements of the solubility of (2) in (1) at 298 K by an analytical method. Il'in et al.3 studied the solubility of (2) in (1) between 283 K and 333 K by analytical method.
At the one temperature (298 K) where comparison is possible, the three studies are in good agreement. These values x2 = 0,0052, x2 = 0,00501 and x2 = 0,00523. These data give an average x2 = 0.0051 ±0.0001 (100 w2 = 2.03), which is recommended. Accordingly, all the available data (see the relevant data sheets) must be regarded as very tentative.
References:

1 Walden, P.; Z. Phys. Chem. 55U, 683-720 (1906).
2 Varlamova, T. M.; Il'in, K. K.; Demakhin, A. G.; Nikurashina, N. I.; Zh. Fiz. Khim. 58, 2730-5 (1984).
3 Il'in, K. K.; Varlamova, T. M.; Lelyukhin, S. V.; Phase Equilibriums and Thermal Analysis (in Russian), Perm', 124 (1988).