Principal English Translation: 

because of; through; on behalf of (see Karttunen and Lockhart)

Frances Karttunen: 

-PAMPA compound postposition for, for the sake of, through, because of / por, por amor, a causa de (S) See -PAN, -PA.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 186.

Lockhart’s Nahuatl as Written: 

relational word. on account of, because of, on behalf of, concerning, for. -pan, -pa.
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 229.

Attestations from sources in English: 

nopampa = because of me; on my behalf
ipampa = because of (anyone or thing)
ipampa = for this reason

Attestations from sources in Spanish: 

nopampa = por mí
ipampa = por él, por ello, porque
mopampatzin = por tí
Rebecca Horn's notes from Nahuatl classes with James Lockhart, now in the possession of Stephanie Wood.