Valve adjustment first.

How about a small Air Leak?

Is your idle speed within the amount on the Emission Sticker?

Maybe the Rack Damper Screw is now broke in and needs re-adjustment.
Briefly remove your Oil Fill Cap; if this improves things your Crank Case Pressure is effecting your Vacuum Shutoff Valve.

Briefly Pinch off your Cigar/Fuel Return Hose; this should raise the Fuel Supply Pressure to the Fuel Injection Pump. If this improves things it is likely your Return/Overflow Valve is not holding the pressure well; a long thread started by Cervan on that.

Or, it could also could be a Fuel Supply Pump issue.

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84 300D, 82 Volvo 244Gl Diesel