IIWM, I would switch fuel lines from in to out, or run off some fuel in a jug under the hood, just to be sure to rule out a tank delivery issue. My tank screen clogged really bad, and the symptom was more like "bogging" rather than surging--low power across the band with no real bucking. But what the heck, it's an easy thing to do.
I'd also get a boost guage and bypass the overboost switch (or whatever they call that thing) on the firewall.
Could a sticky wastegate or overboost solenoid cause "surging"?
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1998 E300D, 287k, barely broken in.
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