diff --git a/lib/core/base/rule.js b/lib/core/base/rule.js
index f12cdbd6..046a8189 100644
--- a/lib/core/base/rule.js
+++ b/lib/core/base/rule.js
@@ -310,11 +310,39 @@ Rule.prototype.run = function run(context, options = {}, resolve, reject) {
     if (options.performanceTimer) {
       this._logRulePerformance();
     }
-    // Defer the rule's execution to prevent "unresponsive script" warnings.
-    // See https://github.com/dequelabs/axe-core/pull/1172 for discussion and details.
-    setTimeout(() => {
+    // [a11y-core]: runTypeASync ON resolves synchronously; OFF keeps the
+    // deferred setTimeout(0) resolve (Deque #1172) and records yield delay.
+    if (cache.get('runTypeASync')) {
       resolve(ruleResult);
-    }, 0);
+    } else {
+      let scheduledAt;
+      try {
+        scheduledAt = window.performance.now();
+      } catch {
+        scheduledAt = undefined;
+      }
+      setTimeout(() => {
+        try {
+          if (scheduledAt !== undefined) {
+            const yieldDelay = window.performance.now() - scheduledAt;
+            const yieldStats = axe._typeASyncYield || {
+              totalMs: 0,
+              count: 0,
+              maxMs: 0
+            };
+            yieldStats.totalMs += yieldDelay;
+            yieldStats.count += 1;
+            if (yieldDelay > yieldStats.maxMs) {
+              yieldStats.maxMs = yieldDelay;
+            }
+            axe._typeASyncYield = yieldStats;
+          }
+        } catch {
+          // ignore instrumentation failures
+        }
+        resolve(ruleResult);
+      }, 0);
+    }
   }).catch(error => {
     if (options.performanceTimer) {
       this._logRulePerformance();