It's been too long since I've had something on the Benz to compulsively worry about ... so I've found something new to overfocus on ...

I've mentioned this before as the car has done it on occasion starting a couple months ago. Occasionally when I come to a stop (or as I am decelerating), the idle speed tends to sort of "hang" at 1000 rpm (and sounds as if it's straining a little) and then slowly drops down to normal idle speed (assuming I don't accelerate, obviously). I've also noticed that while coasting, sometimes it drops down to normal idle fairly fast, while other times it hangs around 1000 and then creeps down to normal. It did this several times as I drove it around to day, but not every time I stopped or slowed down. I've been keeping an eye out for this issue since it did it the first time about two months ago. Most of the time it only does it while the engine is half warmed up, but today it did it a couple of times even when completely warm.

I've been doing as many searches as possible and from what I gather this could be A) sticky throttle linkage or B) a timing problem. Are there any other symptoms or clues I should look for to determine which one it is? I haven't checked out the throttle linkage because, to be very honest, I have no idea where to look or what to look for.

If I bat my eyes and look pretty, will someone offer some advice?

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

Mine does the exact same thing, and when I posted a thread on here awhile ago just about every big poster here with an SDL said theirs' does the same thing. Someone mentioned something about probably having to do with the EDS, Electronic Diesel System. Whatever the electronic piece that controls the idle on the 603--idle is electrically controlled on a 603 while mechanically on a 617--it is probably what is causing your problems. I would bet that if you take out whatever magical box controls the idle, and resoldered all the connections, it would perform flawlessly. I however have bigger things to worry about on my SDL and since the problem is intermittent, you will not really know if it is fixed. If it keeps happening a lot (i.e. several times a day) than perhaps then you should look deeper into it. Otherwise, do not lose too much sleep over it.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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I'm in agreement with David on this one. There is not all that much linkage on the 603 to cause binding, and, if it were binding, there is no good reason for it to return to a proper idle speed.

It's probably the EDS doing some strange behavior. The '86 hasn't exhibited this as of yet. The '87 is too new to evaluate.

Remember that it won't fully come down to idle unless the vehicle is almost stopped. Above a stop, the driveline will backdrive the engine somewhat and the engine will stay above curb idle. This is similar to removing your right foot at 60 mph. The engine sticks at about 2400 rpm until the vehicle slows. Naturally the effect is significantly less at lower speeds.

You could always unplug your EDS unit from the back of the injection pump (the idle will most likely be much lower) but this way you can see if it is consistantly lower or if you still have that "hang" issue.

That would probably annoy me too becuase I dislike inconsistancies. Even my 1969 VW bug comes to a dead exact idle every single time. Anything less than perfection in german automobiles is unacceptable!!!!

Did you guys ever find what is causing this?

I am just finishing replacement of my fuel injection pump, and the (used) replacement pump causes the linkages to hang at an intermediate point, then slide on down to idle if I jiggle it. Whatever it is, it's inside the replacement pump, as with everything disconnected from its linkages, the pump lever does this.

Wondering if it was your problem too, and if anyone else out there has seen this issue.

Thanks,
Gerry

Hello all,
Am glad to be back after a several year forced absence (no, not prison, lol). But now my 83 240d won't stay running after I carefully removed linkage portions behind the air cleaner just to check out the wear on the various plastic pieces. The car will not stay running and the manuals don't show the correct position to reinstall to make it run. Plus the fast idle adjustment cable needs adjustment/replacing. I bought this 123 recently from someone who clearly didn't understand how to maintain it after he got it from his late mother's estate, she was the original owner.

So: who's got a selection of plastic grommets or new spares to buy? Where can I find the liosting since the little books don't tell and I don't have the 123 parts book (need one of those too).

Thanks,
Strelnik