japimport
Active Member
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- The Emerald Isle
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- mercedes c200 sport,mercedes c200 elegance.
hi there just looking to find out what my car should be idling at its a c200 sport 95 and it has no air conditioning
Ian B Walker
MB Enthusiast
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- Jun 7, 2003
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- 7,668
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- 300-24, saloon and coupe, E300 24 valve diesel estate
If memory serves me right between 750 and 850rpm.
Ian B Walker
MB Enthusiast
- Joined
- Jun 7, 2003
- Messages
- 7,668
- Location
- Freckleton
- Car
- 300-24, saloon and coupe, E300 24 valve diesel estate
Its because there is no load from the torque converter when in park. The box is in neutral so to speak. I may be wrong though.
Number_Cruncher
Active Member
It's desirable to have as low a tick over speed as possible, both for environmental / fuel consumption / noise / comfort reasons as well as to reduce creep when stationary in drive.
While the gearbox is in neutral, the torque convertor, fluid, and gearbox input shaft will largely be rotating all as one unit, and the only real external load on the engine is from the drive belts at the front, and the gearbox oil pump at the rear of the crank. There's relatively little damping of engine speed fluctuations by these loads.
However, when you put the gearbox into drive, the input shaft stops rotating, and suddenly, the engine sees both an increase in load (which the idle controller can compensate for), and also an increase in the damping effect of the fluid that is now being stirred up with the difference in speed between the internal parts of the torque convertor.
So, just when it's desirable to reduce engine speed to reduce creep, the engine becomes better damped, and so the idle speed reduction can happen without upsetting the passengers by being felt as a noise, vibration, or harshness.
While the gearbox is in neutral, the torque convertor, fluid, and gearbox input shaft will largely be rotating all as one unit, and the only real external load on the engine is from the drive belts at the front, and the gearbox oil pump at the rear of the crank. There's relatively little damping of engine speed fluctuations by these loads.
However, when you put the gearbox into drive, the input shaft stops rotating, and suddenly, the engine sees both an increase in load (which the idle controller can compensate for), and also an increase in the damping effect of the fluid that is now being stirred up with the difference in speed between the internal parts of the torque convertor.
So, just when it's desirable to reduce engine speed to reduce creep, the engine becomes better damped, and so the idle speed reduction can happen without upsetting the passengers by being felt as a noise, vibration, or harshness.
