Hey all,

Long time lurker, first time poster. Hoping somebody here can shine some light on this very odd issue.

Intro:

I have a very confusing issue on this 2002 S500 (W220). A few months back, i was cleaning under the hood and accidentally pulled on a vacuum line to the Secondary Air Pump system and broke two vacuum lines. I was too irritated to fix it right away and forgot about it over time. Except for the small vacuum leak due to the open tube and a check engine light for the Secondary Air Injection system, car ran fine with no other codes.

Problem/Confusion:

Here is the problem : I am in Texas and we have yearly emission testing which is due now on this car. It won't pass with the CEL. If I leave the secondary air injection vacuum tube disconnected, the car will run fine and I/M Readiness indicators will all go ready except when it comes to the Secondary Air system, it fails and sets the Check Engine light after driving for a day or sometimes 2-3 days. If I connect the vacuum hoses to the SA system, the engine will set Multiple Misfire, Random Misfire and randomly anything from cylinder 3, 4 , 7 misfire within MINUTES of driving.

I can hear the air pump running immediately after cold start and then occasionally during extended idling... so I know the pump is working. I couldn't hear any other vacuum leaks once the SA lines (vacuum) are connected.

What is happening ? How can i fix this? I don't see how air injection (which should be affecting only exhaust pre-cat), is causing misfire and the ECU is NOT detecting any misfire at all every over months of driving with SAI vacuum lines unhooked.

Please guide me.