Spikes, type multimeter in the search and you will find a lot of usefull information. Also search for Led/sw. For a 97 E320, I am not sure if you can check the various modules, with the information you will find with the above searches.
I would focus on the engine control module, this module controls most of the engine functions, including air fuel mixture for various operating temperatures.
Also, these car have a whole bunch of vaccum line, I would make sure everything is connected.
94 E320 58000 Miles