Replacing the air cleaner buffer fixed my idle
 

I was kind of shocked that replacing this part would do more than just keep my air cleaner from rattling. Just thought that I should share this piece of information in case some of you guys are having a hard time getting good idle and you've overlooked the vibration of your air cleaner.

What was wrong / bad about your idle ? .

Do you have a pic? I have no idea what this is.

The idle was rough when the car warmed up to operating temp. The engine felt like it was on the verge of stalling even though the RPMs were at the usual level which is about 825.

Weird. I have a hard time believing a loose air filter would affect idle on a diesel engine.

We are giving you a pass on the initial post since you were asleep at 2 am...
but we still do not know what exactly this thing is you are talking about...
lol

The three 10mm nuts under your air filter go to these: Look for air filter housing mount 1981 Mercedes-Benz 300SD Base Sedan - Intake System - Page 1

I am still shocked and , as others have also mentioned, not convinced this did what it looked like... sometimes things change but not because of the last thing that happened near the car.....

Me too, but what are the chances that it was something else if the problem goes away right after I changed that mount and steady the air cleaner? I've driven the car for about 1/2 hour since replacing the mount and the car is idling like a rock. We'll see if the bad idle comes back later. I hope not.

LIVE LONG ENOUGH and Mechanic ....... 100 percent.

OK - you are talking about the rubber bumpers. Now I see. I have been replacing these for 35 years on my 81SD and have never seen any effect on the idle. In fact I do not buy new ones any more; I drill a hole through the bumper after removing the top and bottom metal screw and plate and insert a long bolt through the entire bumper. Now instead of replacing about every six months to a year, I just about never replace them.

My idle goes from rocking at one stoplight to smooth as glass at the next stoplight to rocking again. Have never been able to figure out why. At some point something just kicks in and it idles smooth as can be but no idea what it is.

But I am pretty sure the buffers/bumpers have no effect on the idle.

:D:D:D

Just like once you fix something, then something else breaks?

Another element to the equation is that the rough idle started a couple of weeks ago when I put 1/3 bottle of Lucus Oil stop leak in the engine(flame suite on) to buy some time on an oil filter housing gasket that I need to replace. The product seemed to helped a little. A week after that, I finished off the bottle and shortly after the idle got rough. I immediately changed the oil with the engine hot. The idle was still bad for another week. I changed the spin on filter and filled it with Diesel Kleen before putting it back on, but that didn't help. I'll post a report in a week or so. If the bad idle comes back sooner, I'll check back.

That's a great idea, I'll have to try that.

Are you talking about a 1981 300SD? Mine has a drop in fuel filter with a bale on top. $10.50 at Pep Boys; changed it this week.

Rough Idle
 

Otto :

That sounds odd to be sure .

When was the last time you cold adjusted the valves ? . everyone thinks because they're quiet , they're fine but they're _NOT_ ~ solid valves require periodic adjustment .

825 RPM's is too high and is prolly masking something else causing the rough idle .