A week ago changed two spark plugs and coils on my 2012 S550. The two were the first two counting from front of the engine on the driver’s side.

The job went fine and the engine ran well but the next day when I went to drive for my trip I got the CEL and first thought “oh s..t. now I have misfire” even I had indexed the plugs correctly.

Hooked up my iCarsoft scanner and it showed no code for misfire but there was a code for “Evaporative purge system flow too low”.

Erased the code and it was fine until the next day. Same code and error message. This time opened the hood with engine running and could hear air leak. With closer inspection I found the problem.

The air tube from the Purge Solenoid Valve has a joint made with just a simple rubber hose. The hard plastic tube ends are just inserted in the rubber hose. In my car this hose is very loose over the plastic tubes and I must have accidentally pushed on the tube while working on my spark plugs and made the connection open.

This all just for info if you have Purge Flow problems. It is a place to look at first as this connection is very odd to see in a Benz. You would think there are clamps over the rubber hose in a connection like this. I added hose clamps so I won’t have issues with it again.

 

Good find. That's a common trouble spot. The rubber hose for the purge valve gets brittle and loose over time. It's tucked right there near the coils, so it's easy to bump during plug changes. Adding those clamps is the exact right fix.