My idle RPMs are a bit low, 600 or so, and I wonder a) can I adjust it and b) is there something that could be causing it to idle lower than 750? trans? fuel supply?

I know the earlier IPs have an adjustment screw, but I don't think the 85 has one.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

after another look, it seems that I do have an adjustment screw.

So. Does it get out of adjustment on it's own, or should I check anything to see if a lower idle is a symptom of something else.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

if the idle has been that way for the duration of your ownership and the idle is not rough in that range... there is no reason to adjust it.

If it has gone during your ownership, there is some troubleshooting to do before adjusting.

If the idle is rough in that range, check fuel connections, and valves (ie.. regular maint.) before adjusting the throttle

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have you messed with the ALDA, that will effect idle speed to a point. Injection timing will also effect idle speed.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

good call, make sure your linkages are set appropriately

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I have adjusted alda, although it is probably back to where it started. I experimented with different settings and it didn't have too much affect unless I cranked it down.

valves were adjusted last July (12K miles ago)

It's always been a little rough at idle. I'll be doing the engine shocks, motor mounts and trans mount this weekend.

I guess I'll tweak it upwards a bit and see if that helps smooth out the idle some

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

try that before you adjust the idle.

If you do adjust the idle be sure not to turn it up anymore than about 800RPM, above 800 the engine isn't governed and it might run away on you.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

My dad's is set to 900, they are governed to about 1100rpm or so, but obviously keep it as low as it will smoothly go. I keep mine around 750-800...I used to have it as low as 550....but idle voltage would drop with accessories on (even with my 80A alternator).....and it would shake when hot. I found the sweet spot and it runs smooooooth now.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

my '82 300td stated to idle at 500 rpm after idling at 700 for years. Also noticed that the doors took along time to lock. Solution : I had a slight vacuum leak in a line under the hood. Fixed the leak and the idle is back at 700 and doors lock fast. The vac leak was partially closing the fuel shut off , giving me the low idle.

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'83 240D 264k on 100% biodiesel/ 31mpg
83 300D 217K the $800 gem
'82 300D 267K the new WVO project car finished and driving for free
International tractor B275 on B100
Ford 555 backhoe on B100
Sargent 25 ton Rough Terrain crane on B50

Which of your vacuum lines was leaking? My door locks are slow, but work, and I've got a shaking at idle.

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)