The idle speed on my 72 450sl is at around 600rpm. The spec calls for 750rpm. The car is well maintained and runs great even at idle with hardly a stumble. Is there a danger in keeping the idle speed so low. Engine coolant temp is perfect and spark plugs show no hint of running too rich or too lean. Car runs fine at idle with the AC on as well.

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1972 450SL
1982 300D Turbo

So why not set it to 750 with the idle speed screw?

Shouldn't hurt anything, but if you have the AC on (idle speed should increase with the AC on because the vac retard should shut off) and the crank the wheels over hard, you may stall the engine.

So long as you have oil pressure, idle speed above 500 is fine. Below that, you risk stalling.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Count your blessings!

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I could easily bring the idle up to 750 if there is a good reason to do so. But if it runs fine at 600 (never stalled) and burns a little less fuel this way why not leave it? Outdoor temp here rarely go below 50~60F so maybe the 750 idle recommend by MB does not apply for me? The AC on--> idle boost works fine.

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1972 450SL
1982 300D Turbo

Go for it!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

When the idle speed is too low the engine vibrates more. This wears out engine mounts.