diesel w123 engine shutoff related to climate control operation
 

Hi- new member just back in the old diesel game with my 1984 300d. I was experiencing a random engine shutoff problem (engine would just stop while I was driving) which I initially thought may be related to the ignition switch assembly and the attached vacuum line for engine shutoff through key use. Previously I had noticed a slight engine stumble when pressing different buttons on my climate control panel, but not severe enough to shut engine off. Yesterday I was able to stop the engine 3 times in succession simply by pressing the farthest right button on the climate control panel (the one with the circle, which shuts climate operation off if I understand correctly). With that button still pressed down, the engine would start, but only run for a few seconds until stopping again. As soon as I pressed a different climate control panel button, I could restart and continue driving without problem. Problem seems intermittent, as in the past I can usually change climate control settings as often as I like, but then when I have stalling issues it happens multiple times in succession before going away. Any ideas? Thank You!

You can quickly determine if you have a vacuum issue causing the shutdown by removing the vacuum line from the shutoff actuator on the injection pump. Try your button pushing again.

If the engine stalls, you have other problems. If it doesn't, it's time to dig into the vacuum line system and figure out where something is crossed. Get a vacuum line diagram and make sure your car matches it.