Is it really a 1983 280SEL? I could only find a listing for a 380SEL from 1983
011 545 came up on PartsShop as a used control unit(011 545 27 32U) for $451.00. I guess the first 6 numbers of a part specify a particular category, so maybe that will help.
Here is what I got as a result when I entered idle control unit for a 1983 380 SEL:
002-545-40-32 Idle Speed Control Relay European from 021545 New 249.90
002-545-40-32+A Idle Speed Control Relay European from 021545 Rebuilt 192.04 Each 93.75(core)
002-545-33-32 Idle Speed Control Unit from '83 New 246.37
002-545-33-32+A Idle Speed Control Unit from '83 Rebuilt 195.89 Each 62.50(core)
002-545-01-32 Idle Speed Control Unit thru '82 New 261.42
002-545-01-32+A Idle Speed Control Unit thru '82 Rebuilt 192.04
If you go to PartsShop fastlane, enter the online catalog, enter your year, model, fuel injection you will see what they list for idle control unit. They do not list Mercedes Parts numbers though. The above information is from another website. I believe the number has probably been updated from 011 to 002.