In this study, an online tuning mechanism for single-input interval type-2 fuzzy PID (OTM-SIT2-FPID) controller has been designed. Interval type-2 fuzzy logic controllers exhibit better performance due to the footprint of uncertainty (FOU) in their interval type-2 fuzzy sets (IT2-FSs). In our study, the FOU was dynamically adjusted online by defining a function which consists of the system error. The system error serves as the input to the OTM-SIT2-FPID controller, while the control signal represents its output. Input variables of the proposed controller are defined by the three triangular interval type-2 fuzzy membership functions, whereas its output variables are characterized by three singleton membership functions. To assess the performance of the proposed controller (OTM-SIT2-FPID), both a single-input interval type-2 fuzzy PID (SIT2-FPID) and a PID controller were also designed. Simulation studies conducted on a nonlinear system under output disturbances demonstrate that the OTM-SIT2-FPID controller exhibits superior robustness and performance compared to the SIT2-FPID and conventional PID controllers.