How do I diagnose an engine that stalls when coming to a stop?
Short answer: Check for codes and idle data, then look at idle air control or throttle body carbon, vacuum leaks, torque converter clutch not releasing, EGR stuck open, and fuel pressure.
Stalling at stops has several common causes. Carbon buildup on the throttle body can restrict idle airflow, so the engine cannot catch itself when the throttle closes. Vacuum leaks cause erratic idle and lean stumbles. A torque converter clutch that does not release drags the engine down like a manual transmission without the clutch pressed. An EGR valve stuck open at idle and low fuel pressure can also cause stalls.
Check for codes and review freeze frame data if available. On a road test, watch idle speed, throttle position, MAF or MAP readings, fuel trims, torque converter clutch command and slip, and EGR position while coming to a stop.
Inspect the throttle body and clean it only if service information allows, then perform an idle relearn. Smoke test for vacuum leaks and check fuel pressure. Have a helper drive while you watch data, never read the screen while driving yourself, and choose a safe, low-traffic route.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.