Need some advice on how to adjust the idle speed on my new 300SDL. It seems that it shakes really good at idle - but especially when cold - I mean it will rattle the hood. When I bring up the idle speed gently with my foot the resonance and the resulting shaking goes away. When I drive, it's smooth as silk, but not so much at idle. Could this problem be caused by bad motor mount(s)?!

So how can I adjust the idle on this car and what should the proper idle be for this car?! I think it's currently hovering around 700-800rpm. It smooths out at about 850-900. Would this proper or too high?!

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

That sounds a bit high.

The W124 FSM has the idle speed for a 603.96/97 at 630 +/- 20 RPM.

I'm not sure whether the W126 has the same type of idle speed control as the W124 (little black knob with numbers on it - I think it's called ELR)

This thread should get you going

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting

Your symptoms are consistent with collapsed engine mounts. Your idle speed is plenty high.....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Regarding engine mounts - how many hex bolts are holding each mount down? I see only one on the outside - is there another one under the heat shield on the 'inside' that I cannot see?! Just wondering in case I jump on doing that job - I did it on my 300D and it was not bad, but the passenger side mount access looks pretty tight...

There are 2 engine mounts on this car, not four - right?!

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Let me ask it another way: is there a how-to on replacing motor-mounts on a 603 engine? All I found is 617 (which I've already done on my other car) - is it just like that on my 300D?!

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Once you have the new mounts and look at them, it'll be pretty self explanitory. There is one mount per side (two socket head from top, one hex from the bottom), and one at the back of the tranny. Don't forget to disconnect the shocks.

BUY DEALER MOUNTS. After I replaced mine (with reputable aftermarket) I heard grumbling from MBCA.org that the rubbers aren't necessarily the same. Even with new injectors I have a shakey idle. Bah!

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k

So there are 3 mounts total, then - including the transmission one it sounds like it?! I should probably replace the transmission mount as well, eh? Wasn't planning on it but if I should then I will...

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

All the rubber is the same age--glassy and trashy (and not the good kind, like a one-night stand). 2x engine, 1x trans.

__________________
James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k