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.

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Zafar
94 E320 58000 Miles