14 hwy on an M119?

Check your o2 sensor, coolant temp sensor (I think? Sensor on the front of the block up top, poke around on the forum), and certainly, the air mass meter

These 3 together solved same problem on my 400E

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL