Is it possible that a glow plug with a high resistence can cause a rough idle that would make the car seem to be "dropping a cylinder"?

I'm supposed to take mine in Friday to the Mercedes dealership (it's under dealer warranty for a few more days) for a rough idle that my mechanic says is not normal and doesn't appear to be bad diesel related. I talked to the service writer and he said a tech thought that a bad GP may be the culprit. I thought that weird as I was under the impression that GP's only started the car (I am far from a mechanic, as that statement may imply).

Any thoughts?

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