FAR Part 13 applies for IDIQ contracts valued within the applicable dollar thresholds (typically $250K, or $7.5 million for commercial items). We know this because there is no exception for indefinite-delivery contracts in FAR 13.002 (Purpose) or 13.003 (Policy). What may be causing some confusion is FAR 13.003(a)(2), which states: 

Agencies shall use simplified acquisition procedures to the maximum extent practicable for all purchases of supplies or services not exceeding the simplified acquisition threshold (including purchases at or below the micro-purchase threshold). This policy does not apply if an agency can meet its requirement using-

           (2) Existing indefinite delivery/indefinite quantity contracts

The fair and reasonable determination policy in FAR Part 13 applies to basic IDIQ awards within the applicable dollar thresholds in FAR Part 13. For DOD, it also applies to individual orders placed against Federal Supply Schedule contracts (see Class Deviation 214-O0011) within the thresholds. The only times FAR Part 13 would not apply is for the basic IDIQ contract, or for task orders placed against FSS contracts, that are above the applicable FAR Part 13 dollar thresholds. In those cases, FAR Part 15 pricing policy applies.