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It does go from 4-3-2-1 but it still gets distributed fairly evenly. Each runner is pulling in EGR gas on the intake stroke only. That means that #1 runner pulls first (the farthest one from the EGR), then #2, then #4, then #3, the firing order of our D15Z1.
But if one of the ports are clogged that go to the runner, then the distribution would not be equal and there would be noticeable hesitation. The same could be said if the entire passage was clogged (not feeding any cylinders) or if the EGR were stuck closed. the ECU adjusts fueling to compensate for the EGR gasses flowing into the cylinders. If the ECU adjusts, but no gases are present, that can make for hesitation/sputtering as well. Same thing if the EGR is stuck open and gasses are present when they shouldn't be.
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