Whenever I am stopped or going slow and I turn the steering wheel all the way (left or right), the RPMs drop from 600 to 500 for a brief second. Why is this? At first I thought it was the resistance when the wheel is turned all the way (more force to move needed to move car), but it does it when the car is stopped also. Is the power steering pump just sucking more power from the engine??
I am not alarmed and don't think anything is wrong, just curious.

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

When pushed to the limit power steering can draw upto 6 hp! Takes a few milliseconds for the idle computer to catch up to this sudden power draw! When you turn the A/C on the pushbutton sends a signal to the idle ECU a few milliseconds before the compressor comes so that it doesn't kill the engine.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

.............and thats when the idle control unit comes into play

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1990 220TE
1988 300GD
1989 yamaha V-MAX(sold)
1993 BMW R100R
1956 Willys Jeep(low bonnet)
1982 Honda XL 250
1987 300D
1994 toyota surf (4runner)2.4 TD EFI
1953 Land Rover