Will iac valve cause vehicle to stall and not start?

Yes, a malfunctioning Idle Air Control (IAC) valve can cause a vehicle to stall and may prevent it from starting. The IAC valve regulates the engine's idle speed by controlling airflow, and if it fails, it can lead to erratic idle behavior or stalling when the engine is at rest. In some cases, if the valve is stuck closed, the engine may not receive enough air to start or run properly.