diff --git a/PDP10/pdp10_cpu.c b/PDP10/pdp10_cpu.c
index 2e08155e..60e00e9f 100644
--- a/PDP10/pdp10_cpu.c
+++ b/PDP10/pdp10_cpu.c
@@ -194,7 +194,6 @@ int32 stop_op0 = 0;                                     /* stop on 0 */
 int32 rlog = 0;                                         /* extend fixup log */
 int32 ind_max = 0;                                      /* nested ind limit */
 int32 xct_max = 0;                                      /* nested XCT limit */
-int32 t20_idlelock = 0;                                 /* TOPS-20 idle lock */
 a10 pcq[PCQ_SIZE] = { 0 };                              /* PC queue */
 int32 pcq_p = 0;                                        /* PC queue ptr */
 REG *pcq_r = NULL;                                      /* PC queue reg ptr */
@@ -650,7 +649,6 @@ rlog = 0;                                               /* not in extend */
 pi_eval ();                                             /* eval pi system */
 if (!Q_ITS)                                             /* ~ITS, clr 1-proc */
     its_1pr = 0;
-t20_idlelock = 0;                                       /* clr T20 idle lock */
 
 /* Abort handling
 
@@ -1153,7 +1151,7 @@ case 0341:  AOJ; if (TL (AC(ac))) JUMP (ea); break;     /* AOJL */
 case 0342:  AOJ; if (TE (AC(ac))) JUMP (ea); break;     /* AOJE */
 case 0343:  AOJ; if (TLE (AC(ac))) JUMP (ea); break;    /* AOJLE */
 case 0344:  AOJ; JUMP(ea);                              /* AOJA */
-            if (Q_ITS && Q_IDLE &&                      /* ITS idle? */
+            if (Q_ITS &&                                /* ITS idle? */
                 TSTF (F_USR) && (pager_PC == 017) &&    /* user mode, loc 17? */
                 (ac == 0) && (ea == 017))               /* AOJA 0,17? */
                 sim_idle (0, FALSE);
@@ -1177,19 +1175,13 @@ case 0364:  SOJ; JUMP(ea); break;                       /* SOJA */
 case 0365:  SOJ; if (TGE (AC(ac))) JUMP (ea); break;    /* SOJGE */
 case 0366:  SOJ; if (TN (AC(ac))) JUMP (ea); break;     /* SOJN */
 case 0367:  SOJ; if (TG (AC(ac))) JUMP (ea);            /* SOJG */
-            if ((ea == pager_PC) && Q_IDLE) {           /* to self, idle enab? */
-                extern int32 tmr_poll;
+            if (ea == pager_PC) {                       /* to self? */
                 if ((ac == 6) && (ea == 1) &&           /* SOJG 6,1? */
                     TSTF (F_USR) && Q_T10)              /* T10, user mode? */
-                    sim_idle (0, FALSE);
-                else if (!t20_idlelock &&               /* interlock off? */
-                    (ac == 2) && (ea == 3) &&           /* SOJG 2,3? */
-                    !TSTF (F_USR) && Q_T20 &&           /* T20, mon mode? */
-                    (sim_interval > (tmr_poll >> 1))) { /* >= half clock? */
-                    t20_idlelock = 1;                   /* set interlock */
-                    if (sim_os_ms_sleep (1))            /* sleep 1ms */
-                        sim_interval = 0;               /* if ok, sched event */
-                    }
+                    sim_idle (0, FALSE);                /* idle */
+                else if ((ac == 2) && (ea == 3) &&      /* SOJG 2,3? */
+                    !TSTF (F_USR) && Q_T20)             /* T20, mon mode? */
+                    sim_idle (0, FALSE);                /* idle */
                 }                    
             break;
 case 0370:  SOS; break;                                 /* SOS */
diff --git a/PDP10/pdp10_defs.h b/PDP10/pdp10_defs.h
index fa37e24b..e6a86309 100644
--- a/PDP10/pdp10_defs.h
+++ b/PDP10/pdp10_defs.h
@@ -140,7 +140,6 @@ typedef t_int64         d10;                            /* PDP-10 data (36b) */
 #define Q_ITS           (cpu_unit.flags & UNIT_ITS)
 #define Q_T20           (cpu_unit.flags & UNIT_T20)
 #define Q_KLAD          (cpu_unit.flags & UNIT_KLAD)
-#define Q_IDLE          (sim_idle_enab)
 
 /* Architectural constants */
 
diff --git a/PDP10/pdp10_tim.c b/PDP10/pdp10_tim.c
index b0f0cd9b..708bfc00 100644
--- a/PDP10/pdp10_tim.c
+++ b/PDP10/pdp10_tim.c
@@ -132,7 +132,6 @@ static d10 tim_new_period = 0;                          /* period for the next i
 static int32 tim_mult;                                  /* Multiple of interval timer period at which tmxr is polled */
 
 d10 quant = 0;                                          /* ITS quantum */
-static int32 tim_t20_prob = 33;                         /* TOPS-20 prob */
 
 /* Exported variables - initialized by set CPU model and reset */
 
@@ -144,7 +143,6 @@ extern int32 apr_flg, pi_act;
 extern UNIT cpu_unit;
 extern d10 pcst;
 extern a10 pager_PC;
-extern int32 t20_idlelock;
 
 static t_stat tcu_rd (int32 *data, int32 PA, int32 access);
 static t_stat tim_svc (UNIT *uptr);
@@ -175,7 +173,6 @@ static REG tim_reg[] = {
     { ORDATAD (PERIOD, tim_period, 36, "reset value for interval") },
     { ORDATAD (QUANT, quant, 36, "quantum timer (ITS only)") },
     { DRDATAD (TIME, tim_unit.wait, 24, "tick delay"), REG_NZ + PV_LEFT },
-    { DRDATA (PROB, tim_t20_prob, 6), REG_NZ + PV_LEFT + REG_HIDDEN },
     { DRDATA (POLL, tmr_poll, 32), REG_HRO + PV_LEFT },
     { DRDATA (MUXPOLL, tmxr_poll, 32), REG_HRO + PV_LEFT },
     { DRDATA (MULT, tim_mult, 6), REG_HRO + PV_LEFT },
@@ -341,12 +338,14 @@ return FALSE;
 
 static t_stat tim_svc (UNIT *uptr)
 {
-if (cpu_unit.flags & UNIT_KLAD)                         /* diags? */
+if (cpu_unit.flags & UNIT_KLAD) {                       /* diags? */
     tmr_poll = uptr->wait;                              /* fixed clock */
-else
+    sim_activate (uptr, tmr_poll);                          /* reactivate unit */
+    }
+else {
     tmr_poll = sim_rtc_calb (clk_tps);                  /* else calibrate */
-    
-sim_activate (uptr, tmr_poll);                          /* reactivate unit */
+    sim_activate_after (uptr, 1000000/clk_tps);         /* reactivate unit */
+    }
 tmxr_poll = tmr_poll * tim_mult;                        /* set mux poll */
 tim_incr_base (tim_base, tim_period);                   /* incr time base based on period of expired interval */
 tim_period = tim_new_period;                            /* If interval has changed, update period */
@@ -360,10 +359,6 @@ if (Q_ITS) {                                            /* ITS? */
         pcst = AOB (pcst);                              /* add 1,,1 */
         }
     }                                                   /* end ITS */
-else {
-    if (t20_idlelock && PROB (100 - tim_t20_prob))
-        t20_idlelock = 0;
-    }
 return SCPE_OK;
 }