My 96 SL320 has done this twice. Everytime I do anything minor to the engine it goes into limp mode. The first time I replaced the plugs and cleaned the engine, it went into limp and CE came on. I disconnected the battery while servicing replacing the valve cover gasket and when I reconnected it the light went out. I cleaned my engine last weekend, removed all the plastic parts and used degreaser, even the undercarriage, I also cleaned the intake manifold with a cleaner, afterward I was driving the car and it started to miss, the engine light came on. Again I pulled over turned the car off and immediatly re-started. The engine has been fine since. Maybe when I disconnect the devices from the breather tube? maybe when wet? is my car known to have this dreaded harness issue? It is like a gremlin in there, I never know what to expect! All my MB's have had their little personalities!