diff --git a/cluster.go b/cluster.go
index 4ed29bea1..a0da8d3bb 100644
--- a/cluster.go
+++ b/cluster.go
@@ -33,9 +33,10 @@ import (
 	"sync"
 	"time"
 
-	"gopkg.in/mgo.v2-unstable/bson"
 	"strconv"
 	"strings"
+
+	"gopkg.in/mgo.v2-unstable/bson"
 )
 
 // ---------------------------------------------------------------------------
@@ -122,10 +123,10 @@ func (cluster *mongoCluster) removeServer(server *mongoServer) {
 	other := cluster.servers.Remove(server)
 	cluster.Unlock()
 	if other != nil {
-		other.Close()
+		other.CloseIdle()
 		log("Removed server ", server.Addr, " from cluster.")
 	}
-	server.Close()
+	server.CloseIdle()
 }
 
 type isMasterResult struct {
diff --git a/cluster_test.go b/cluster_test.go
index 524acbc93..ea09feb3f 100644
--- a/cluster_test.go
+++ b/cluster_test.go
@@ -27,11 +27,13 @@
 package mgo_test
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"net"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	. "gopkg.in/check.v1"
@@ -1477,7 +1479,6 @@ func (s *S) TestSecondaryModeWithMongosInsert(c *C) {
 	c.Assert(result.A, Equals, 1)
 }
 
-
 func (s *S) TestRemovalOfClusterMember(c *C) {
 	if *fast {
 		c.Skip("-fast")
@@ -2088,3 +2089,72 @@ func (s *S) TestDoNotFallbackToMonotonic(c *C) {
 		c.Assert(q13b, Equals, q13a)
 	}
 }
+
+func (s *S) TestConnectServerFailed(c *C) {
+	dials := int32(0)
+	maxDials := 50
+	info := &mgo.DialInfo{
+		Addrs: []string{"localhost:40001"},
+		DialServer: func(addr *mgo.ServerAddr) (net.Conn, error) {
+			n := atomic.AddInt32(&dials, 1)
+			if n == int32(maxDials/2) {
+				return nil, errors.New("expected dial failed")
+			}
+			return net.Dial("tcp", addr.String())
+		},
+	}
+
+	session, err := mgo.DialWithInfo(info)
+	c.Assert(err, IsNil)
+	defer session.Close()
+
+	mgo.ResetStats()
+
+	errs := make(chan error, 1)
+	var done int32
+	var finished sync.WaitGroup
+	var starting sync.WaitGroup
+	defer func() {
+		atomic.StoreInt32(&done, 1)
+		finished.Wait()
+	}()
+	for i := 0; i < maxDials; i++ {
+		finished.Add(1)
+		starting.Add(1)
+		go func(s0 *mgo.Session) {
+			defer finished.Done()
+			for i := 0; ; i++ {
+				if atomic.LoadInt32(&done) == 1 {
+					break
+				}
+				err := func(s0 *mgo.Session) error {
+					s := s0.Copy()
+					defer s.Close()
+					coll := s.DB("mydb").C("mycoll")
+
+					var ret []interface{}
+					return coll.Find(nil).All(&ret)
+				}(s0)
+				if err != nil {
+					select {
+					case errs <- err:
+					default:
+					}
+				}
+				if i == 0 {
+					starting.Done()
+				}
+			}
+		}(session)
+		time.Sleep(10 * time.Millisecond)
+	}
+	starting.Wait()
+
+	// no errors expect.
+	var opErr error
+	select {
+	case opErr = <-errs:
+	default:
+	}
+	c.Assert(opErr, IsNil)
+}
diff --git a/server.go b/server.go
index ba0480e58..8ae789aa5 100644
--- a/server.go
+++ b/server.go
@@ -187,6 +187,16 @@ func (server *mongoServer) Connect(timeout time.Duration) (*mongoSocket, error)
 // Close forces closing all sockets that are alive, whether
 // they're currently in use or not.
 func (server *mongoServer) Close() {
+	server.close(false)
+}
+
+// CloseIdle closing all sockets that are idle,
+// sockets currently in use will be closed after idle.
+func (server *mongoServer) CloseIdle() {
+	server.close(true)
+}
+
+func (server *mongoServer) close(waitForIdle bool) {
 	server.Lock()
 	server.closed = true
 	liveSockets := server.liveSockets
@@ -196,7 +206,11 @@ func (server *mongoServer) Close() {
 	server.Unlock()
 	logf("Connections to %s closing (%d live sockets).", server.Addr, len(liveSockets))
 	for i, s := range liveSockets {
-		s.Close()
+		if waitForIdle {
+			s.CloseAfterIdle()
+		} else {
+			s.Close()
+		}
 		liveSockets[i] = nil
 	}
 	for i := range unusedSockets {
diff --git a/socket.go b/socket.go
index a2343354d..9783136e0 100644
--- a/socket.go
+++ b/socket.go
@@ -40,19 +40,20 @@ type replyFunc func(err error, reply *replyOp, docNum int, docData []byte)
 
 type mongoSocket struct {
 	sync.Mutex
-	server        *mongoServer // nil when cached
-	conn          net.Conn
-	timeout       time.Duration
-	addr          string // For debugging only.
-	nextRequestId uint32
-	replyFuncs    map[uint32]replyFunc
-	references    int
-	creds         []Credential
-	logout        []Credential
-	cachedNonce   string
-	gotNonce      sync.Cond
-	dead          error
-	serverInfo    *mongoServerInfo
+	server         *mongoServer // nil when cached
+	conn           net.Conn
+	timeout        time.Duration
+	addr           string // For debugging only.
+	nextRequestId  uint32
+	replyFuncs     map[uint32]replyFunc
+	references     int
+	creds          []Credential
+	logout         []Credential
+	cachedNonce    string
+	gotNonce       sync.Cond
+	dead           error
+	serverInfo     *mongoServerInfo
+	closeAfterIdle bool
 }
 
 type queryOpFlags uint32
@@ -264,10 +265,13 @@ func (socket *mongoSocket) Release() {
 	if socket.references == 0 {
 		stats.socketsInUse(-1)
 		server := socket.server
+		closeAfterIdle := socket.closeAfterIdle
 		socket.Unlock()
 		socket.LogoutAll()
-		// If the socket is dead server is nil.
-		if server != nil {
+		if closeAfterIdle {
+			socket.Close()
+		} else if server != nil {
+			// If the socket is dead server is nil.
 			server.RecycleSocket(socket)
 		}
 	} else {
@@ -316,6 +320,21 @@ func (socket *mongoSocket) Close() {
 	socket.kill(errors.New("Closed explicitly"), false)
 }
 
+// CloseAfterIdle terminates an idle socket, which has a zero
+// reference, or marks the socket to be terminate after idle.
+func (socket *mongoSocket) CloseAfterIdle() {
+	socket.Lock()
+	if socket.references == 0 {
+		socket.Unlock()
+		socket.Close()
+		logf("Socket %p to %s: idle and close.", socket, socket.addr)
+		return
+	}
+	socket.closeAfterIdle = true
+	socket.Unlock()
+	logf("Socket %p to %s: close after idle.", socket, socket.addr)
+}
+
 func (socket *mongoSocket) kill(err error, abend bool) {
 	socket.Lock()
 	if socket.dead != nil {