Idle has been fine since the last 10 years.
Recently, I can't keep the foot of the pedal after firing up the engine in cold condition. It does ok once the engine has some temperature. But still, idle feels a little low, compared to what it was.

Where can I adjust the idle RPM?

I would be more suspicious of a couple of glow plugs about to go than too low idle.

However:https://www.startekinfo.com/StarTek/outside/12253/program/Engine/617/30-300.pdf

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Sam

84 300SD 350K+ miles ( Blue Belle )

Doesn't seem to be a glow plug issue on this one. It fires right up. No delay whatsoever.

It might be an issue on the other car I have with the same powertrain.
It's cranking too much. It wouldn't fire unless I do 2x pre-glow cycles with just a couple of crank rotations in between.

I first suspected a drop in fuel pressure while the car is parked over night. But I think it may not pre-glow on all 5.

Could be a gummed up governor. I fixed mine with some cleaner in the fuel.
It took two tanks and the good idle slowly came back.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

If you have an MW Fuel Injecting Pump the idle speed is changed by backing off the Rack Damper/Governor Idle/Rack Dampner Pin and then on the Engine side of the Fuel Injection Pump look down and you will see a screw with a screwdrivers slot and below a 14mm Nut to lock it.
There is other methods to loosen the 14mm nut.

I use a 14mm Crows Foot on an extension to loosen and tighten the Nut and a Scrwdriver on the screw.

Once our idle speed is set you need to slowly back in the Rack Damper/Governor Idle/Rack Dampner Pin. The idea is to remove as much engine shake at the same time barely effecting the idle speed or not at all effecting the idle speed.

The pic with the large yellow arrow points to the Rack Damper/Governor Idle/Rack Dampner Pin.

Attached Thumbnails

     

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84 300D, 82 Volvo 244Gl Diesel

Thanks, I already located the adjustment screw with the 14mm nut. I can also see the rack damper. Have to find a way to loosen the 14mm nut.

Engine shakes just a little when warm in idle.

My '81 was like that. Had to keep it revved for a minute to back out of the garage. Needed a valve adjustment. Solved the problem.