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!)