Author Topic: Engine RPM hunting under light load while warming up  (Read 2661 times)

beachbear

  • Full Member
  • Regular
  • **
  • USA, HI, Kailua
  • Posts: 65
Engine RPM hunting under light load while warming up
« on: May 09, 2016, 00:45:23 »
Usually experienced after a few minutes of running, while coming to a stop or slowing to round a corner; my '69 automatic "hunts for an idle speed", seeming to die, then surging in waves of unnerving bucks. If I move the shifter to 3rd as I decelerate, I can usually avoid this as I force the engine to assist in braking the car's speed. I have almost no trouble starting the motor. I do usually have to give it a couple of seconds on a "first of the day crank", then rotate the ignition switch OFF and back, but then it starts and runs smoothly. But I believe this is a separate, and less annoying issue. I live in a warm climate, so the engine coolant starts around 72 degrees F. After about 5-10 miles of average city driving, the engine and transmission work together as they should. I've looked at the various components that assist warmup, and shifting, but none seem to relate directly to this issue. Have any of you experienced and/or solved something like this?
David White
'69 280sl automatic, 3rd owner since '82

Benz Dr.

  • Associate Member
  • Platinum
  • ******
  • Canada, ON, Port Lambton
  • Posts: 7220
  • Benz Dr.
Re: Engine RPM hunting under light load while warming up
« Reply #1 on: May 09, 2016, 01:00:37 »
Kind of sounds like a fuel mixture problem or a possible throttle position switch adjustment or even both.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

Cees Klumper

  • Full Member
  • Platinum
  • ******
  • USA, CA, Fallbrook
  • Posts: 5721
    • http://SL113.org
Re: Engine RPM hunting under light load while warming up
« Reply #2 on: May 09, 2016, 16:32:20 »
My wngine started doing the exact same thing years ago, and I've been battling it ever since. I am pretty sure it's the WRD (Won't Run Device, aka Warm Running Device) operation, shims, thermostat or what have you. Am going to remedy for sure this summer!
Cees Klumper
1969 Mercedes 280 SL automatic
1968 Ford Mustang 302 V8
1961 Alfa Romeo Giulietta Sprint Coupe 1600
1962 FIAT 1500S OSCA convertible
1972 Lancia Fulvia Coupe 1.3
1983 Porsche 944 2.5
1990 Ford Bronco II