Flucuating Idle 1984 300sd
 

Lately I have noticed that when my 84 300sd idles in park, the idle speed flucuates. It speeds up then slows down, over and over. Lets say 800 to 900 rpm and back. You can just see it on the tach. Stops if you place the car in drive.

Where should I look?

Can you hear the engine change speed or is it just in the tach? I have read that a lot of problems with the tach come from the tach amplifier mounted on the driver's side inner fender.

The engine speed is actually pulsing up and down.

That's odd. How old are your fuel and air filters?

The idle governor pin (rack dampener bolt) needs to be adjusted. Mine did the same, adjustment of the pin removed the pulsing.

IIRC, if the pin is adjusted too tight, pulsing will happen. Adjust it back out a little.

Idle dampener on the end of the IP maybe? There is a screw there to adjust idle and a spring in the cover. If the spring wears out, it could account for a lopey idle.

MBeige beat me to it.

Lopey idle is the perfect description. I will try adjusting the damper adjustment tonight.

Thanks so much for the suggestions.

Can this be an intermittent problem
 

My '85 300d will have a slight pulse/lope at idle occasionally. It's more visible in the oil pressure gauge than the tach, and goes away when in gear.Haven't tested for any consistent variables because of the infrequency.

Hunting is the term you seek.