failed emmissions test how to correct

Bring it to another shop. I would give it more than one try before i replaced an engine. Before you do, put fuel additive in your tank, something that will break down carbon deposits and run it for a while to clean it out. Also change your oil if you haven't in 3,000 miles. Worth a shot IMO. Give it a tune up to improve combustion or at least put new plugs in it.

there is a additive called seafoam it works, and 1 qt of alcohol % with 1/2 tank of 93 octain run you c180 for 1hr. and take it back if and you will pass emission that old school....................

First test for compresion, its easy and cheap. if compression is ok you will need to check injectors, maf, oxygen sensors etc. when you complete the compression test return here. luck

Get some "Tuneup" additive and put into the fuel. Then run the car with the engine rpm not under 2500, for about 30min. Then you drive it with as high gear and low rpm again for 30 min. ( to make the engine really hot ) and then 30 mins at high rpms again . Works everytime

Take it to Mercedes dealer and get the car fixed right.