Diagnosis
This is often caused by a dirty or faulty RTD temperature probe, not the controller itself. Grease insulates the probe, causing delayed and inaccurate readings that make the controller over-correct.
How to Fix It
Let the grill cool. Locate the RTD probe at the rear of the cook chamber. Remove it by unscrewing the single mounting nut. Clean the probe shaft thoroughly with a soft brass brush and mild detergent to remove all grease and carbon. Rinse and dry completely before reinstalling.
If That Didn't Work
Check for excessive ash in the firepot. A deep ash bed insulates the burn and causes erratic flame output. Before your next cook, vacuum the firepot completely. Ensure the grease management system is clear so heat can convect properly.
Heads Up
Do not rely on the lid thermometer. It can read differently than the digital controller probe. For critical cooks, always use a trusted third-party ambient thermometer on the grill grate for verification.