What is this? 85 300D. My 83 doesn't have it.

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85 300SD. 88 300SE. 85 560SL.

Actually I have not seen anyone ask about that. The 85s had a more than extensive vacuum setup.

There is a vacuum diagram in post 33.

I can only make a wild guess. At the bottom left of the diagram is the EGR #60 and I think the item in your pic is #71 the air recirculating valve. The diagram was not clear enough for me to see the color code of the plastic tubing.

1985 300D vacuum crazyness.

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84 300D, 82 Volvo 244Gl Diesel

Thank you, that's useful info.

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85 300SD. 88 300SE. 85 560SL.

Air Recirculating Valve = ARV.

I asked this a few years back. Rollguy explained it.

Got a 1985 300D turbo

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

My 1985 CA 300D has a similar looking vacuum actuator on the turbopump compressor side (front). Also termed "air-recirculating" (recall), but I don't know the purpose. I capped off the vac port since EGR clutter is gone.

The ARV supposedly reduces boost as the transmission modulator vacuum goes down. You can kind of see the circuit in 911’s diagram above. As modulator vacuum goes up to soften the shift, a vacuum is pulled on the ARV which is kind an internal bypass in the turbo.

At least that’s my best guess in addition to what Rollguy says.

ETA - and I unplugged mine and discarded that part of the vacuum circuit. I didn’t even bother plugging it off since it doesn’t seem to leak turbo pressure. According to the diagram it is open to the atmosphere unless the switchover valve is activated by the EGR computer.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Thank you all, this is great info. I really appreciate it.

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85 300SD. 88 300SE. 85 560SL.