You shouldn't need to plug in a block heater with temps only in the 40's. I believe you are on the right track with a current valve adjustment. The surging is what puzzles me a bit. When was the last main fuel filter change? (spin-on) Possibly water in the fuel? When you do the filter change, dump the old fuel from the previous filter into a see-through jar, let it set for 24 hrs. and look for separation. If the result appears as two layers, then there might be water condensation in the fuel. How much volume of water (ratio to fuel) will determine the next action to take.

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Sam

84 300SD 350K+ miles ( Blue Belle )