diff --git a/services/surfaceflinger/Scheduler/Scheduler.cpp b/services/surfaceflinger/Scheduler/Scheduler.cpp
index 9ea3f35..5ec7e48 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.cpp
+++ b/services/surfaceflinger/Scheduler/Scheduler.cpp
@@ -82,7 +82,7 @@
     mTouchTimer.reset();
 
     // Stop idle timer and clear callbacks, as the RefreshRateSelector may outlive the Scheduler.
-    demotePacesetterDisplay();
+    demotePacesetterDisplay({.toggleIdleTimer = true});
 }
 
 void Scheduler::initVsync(frametimeline::TokenManager& tokenManager,
@@ -118,9 +118,10 @@
 }
 
 void Scheduler::setPacesetterDisplay(PhysicalDisplayId pacesetterId) {
-    demotePacesetterDisplay();
+    constexpr PromotionParams kPromotionParams = {.toggleIdleTimer = true};
 
-    promotePacesetterDisplay(pacesetterId);
+    demotePacesetterDisplay(kPromotionParams);
+    promotePacesetterDisplay(pacesetterId, kPromotionParams);
 }
 
 void Scheduler::registerDisplay(PhysicalDisplayId displayId, RefreshRateSelectorPtr selectorPtr,
@@ -139,16 +140,22 @@
                                         RefreshRateSelectorPtr selectorPtr,
                                         VsyncSchedulePtr schedulePtr,
                                         PhysicalDisplayId activeDisplayId) {
-    demotePacesetterDisplay();
+    const bool isPrimary = (ftl::FakeGuard(mDisplayLock), !mPacesetterDisplayId);
 
-    auto [pacesetterVsyncSchedule, isNew] = [&]() FTL_FAKE_GUARD(kMainThreadContext) {
+    // Start the idle timer for the first registered (i.e. primary) display.
+    const PromotionParams promotionParams = {.toggleIdleTimer = isPrimary};
+
+    demotePacesetterDisplay(promotionParams);
+
+    auto [pacesetterVsyncSchedule, isNew] = [&]() REQUIRES(kMainThreadContext) {
         std::scoped_lock lock(mDisplayLock);
         const bool isNew = mDisplays
                                    .emplace_or_replace(displayId, displayId, std::move(selectorPtr),
                                                        std::move(schedulePtr), mFeatures)
                                    .second;
 
-        return std::make_pair(promotePacesetterDisplayLocked(activeDisplayId), isNew);
+        return std::make_pair(promotePacesetterDisplayLocked(activeDisplayId, promotionParams),
+                              isNew);
     }();
 
     applyNewVsyncSchedule(std::move(pacesetterVsyncSchedule));
@@ -166,7 +173,8 @@
 
     dispatchHotplug(displayId, Hotplug::Disconnected);
 
-    demotePacesetterDisplay();
+    constexpr PromotionParams kPromotionParams = {.toggleIdleTimer = false};
+    demotePacesetterDisplay(kPromotionParams);
 
     std::shared_ptr<VsyncSchedule> pacesetterVsyncSchedule;
     {
@@ -178,7 +186,7 @@
         // headless virtual display.)
         LOG_ALWAYS_FATAL_IF(mDisplays.empty(), "Cannot unregister all displays!");
 
-        pacesetterVsyncSchedule = promotePacesetterDisplayLocked(activeDisplayId);
+        pacesetterVsyncSchedule = promotePacesetterDisplayLocked(activeDisplayId, kPromotionParams);
     }
     applyNewVsyncSchedule(std::move(pacesetterVsyncSchedule));
 }
@@ -917,19 +925,18 @@
     return mFrameRateOverrideMappings.updateFrameRateOverridesByContent(frameRateOverrides);
 }
 
-void Scheduler::promotePacesetterDisplay(PhysicalDisplayId pacesetterId) {
+void Scheduler::promotePacesetterDisplay(PhysicalDisplayId pacesetterId, PromotionParams params) {
     std::shared_ptr<VsyncSchedule> pacesetterVsyncSchedule;
-
     {
         std::scoped_lock lock(mDisplayLock);
-        pacesetterVsyncSchedule = promotePacesetterDisplayLocked(pacesetterId);
+        pacesetterVsyncSchedule = promotePacesetterDisplayLocked(pacesetterId, params);
     }
 
     applyNewVsyncSchedule(std::move(pacesetterVsyncSchedule));
 }
 
 std::shared_ptr<VsyncSchedule> Scheduler::promotePacesetterDisplayLocked(
-        PhysicalDisplayId pacesetterId) {
+        PhysicalDisplayId pacesetterId, PromotionParams params) {
     // TODO: b/241286431 - Choose the pacesetter among mDisplays.
     mPacesetterDisplayId = pacesetterId;
     ALOGI("Display %s is the pacesetter", to_string(pacesetterId).c_str());
@@ -938,15 +945,18 @@
     if (const auto pacesetterOpt = pacesetterDisplayLocked()) {
         const Display& pacesetter = *pacesetterOpt;
 
-        pacesetter.selectorPtr->setIdleTimerCallbacks(
-                {.platform = {.onReset = [this] { idleTimerCallback(TimerState::Reset); },
-                              .onExpired = [this] { idleTimerCallback(TimerState::Expired); }},
-                 .kernel = {.onReset = [this] { kernelIdleTimerCallback(TimerState::Reset); },
-                            .onExpired = [this] { kernelIdleTimerCallback(TimerState::Expired); }},
-                 .vrr = {.onReset = [this] { mSchedulerCallback.vrrDisplayIdle(false); },
-                         .onExpired = [this] { mSchedulerCallback.vrrDisplayIdle(true); }}});
+        if (!FlagManager::getInstance().connected_display() || params.toggleIdleTimer) {
+            pacesetter.selectorPtr->setIdleTimerCallbacks(
+                    {.platform = {.onReset = [this] { idleTimerCallback(TimerState::Reset); },
+                                  .onExpired = [this] { idleTimerCallback(TimerState::Expired); }},
+                     .kernel = {.onReset = [this] { kernelIdleTimerCallback(TimerState::Reset); },
+                                .onExpired =
+                                        [this] { kernelIdleTimerCallback(TimerState::Expired); }},
+                     .vrr = {.onReset = [this] { mSchedulerCallback.vrrDisplayIdle(false); },
+                             .onExpired = [this] { mSchedulerCallback.vrrDisplayIdle(true); }}});
 
-        pacesetter.selectorPtr->startIdleTimer();
+            pacesetter.selectorPtr->startIdleTimer();
+        }
 
         newVsyncSchedulePtr = pacesetter.schedulePtr;
 
@@ -966,11 +976,14 @@
     }
 }
 
-void Scheduler::demotePacesetterDisplay() {
-    // No need to lock for reads on kMainThreadContext.
-    if (const auto pacesetterPtr = FTL_FAKE_GUARD(mDisplayLock, pacesetterSelectorPtrLocked())) {
-        pacesetterPtr->stopIdleTimer();
-        pacesetterPtr->clearIdleTimerCallbacks();
+void Scheduler::demotePacesetterDisplay(PromotionParams params) {
+    if (!FlagManager::getInstance().connected_display() || params.toggleIdleTimer) {
+        // No need to lock for reads on kMainThreadContext.
+        if (const auto pacesetterPtr =
+                    FTL_FAKE_GUARD(mDisplayLock, pacesetterSelectorPtrLocked())) {
+            pacesetterPtr->stopIdleTimer();
+            pacesetterPtr->clearIdleTimerCallbacks();
+        }
     }
 
     // Clear state that depends on the pacesetter's RefreshRateSelector.
diff --git a/services/surfaceflinger/Scheduler/Scheduler.h b/services/surfaceflinger/Scheduler/Scheduler.h
index 4dba6fc..94583db 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.h
+++ b/services/surfaceflinger/Scheduler/Scheduler.h
@@ -377,8 +377,17 @@
     void resyncAllToHardwareVsync(bool allowToEnable) EXCLUDES(mDisplayLock);
     void setVsyncConfig(const VsyncConfig&, Period vsyncPeriod);
 
-    void promotePacesetterDisplay(PhysicalDisplayId pacesetterId) REQUIRES(kMainThreadContext)
-            EXCLUDES(mDisplayLock);
+    // TODO: b/241286431 - Remove this option, which assumes that the pacesetter does not change
+    // when a (secondary) display is registered or unregistered. In the short term, this avoids
+    // a deadlock where the main thread joins with the timer thread as the timer thread waits to
+    // lock a mutex held by the main thread.
+    struct PromotionParams {
+        // Whether to stop and start the idle timer. Ignored unless connected_display flag is set.
+        bool toggleIdleTimer;
+    };
+
+    void promotePacesetterDisplay(PhysicalDisplayId pacesetterId, PromotionParams)
+            REQUIRES(kMainThreadContext) EXCLUDES(mDisplayLock);
 
     // Changes to the displays (e.g. registering and unregistering) must be made
     // while mDisplayLock is locked, and the new pacesetter then must be promoted while
@@ -386,13 +395,16 @@
     // MessageQueue and EventThread need to use the new pacesetter's
     // VsyncSchedule, and this must happen while mDisplayLock is *not* locked,
     // or else we may deadlock with EventThread.
-    std::shared_ptr<VsyncSchedule> promotePacesetterDisplayLocked(PhysicalDisplayId pacesetterId)
+    std::shared_ptr<VsyncSchedule> promotePacesetterDisplayLocked(PhysicalDisplayId pacesetterId,
+                                                                  PromotionParams)
             REQUIRES(kMainThreadContext, mDisplayLock);
     void applyNewVsyncSchedule(std::shared_ptr<VsyncSchedule>) EXCLUDES(mDisplayLock);
 
-    // Blocks until the pacesetter's idle timer thread exits. `mDisplayLock` must not be locked by
-    // the caller on the main thread to avoid deadlock, since the timer thread locks it before exit.
-    void demotePacesetterDisplay() REQUIRES(kMainThreadContext) EXCLUDES(mDisplayLock, mPolicyLock);
+    // If toggleIdleTimer is true, the calling thread blocks until the pacesetter's idle timer
+    // thread exits, in which case mDisplayLock must not be locked by the caller to avoid deadlock,
+    // since the timer thread locks it before exit.
+    void demotePacesetterDisplay(PromotionParams) REQUIRES(kMainThreadContext)
+            EXCLUDES(mDisplayLock, mPolicyLock);
 
     void registerDisplayInternal(PhysicalDisplayId, RefreshRateSelectorPtr, VsyncSchedulePtr,
                                  PhysicalDisplayId activeDisplayId) REQUIRES(kMainThreadContext)