Chevy & GMC Vans

I have a P0134 code and trying to figure out which one it refers to. Might be just due to carbon but I might have to replace it. I have got parts places response anywhere from of 2-4 sensors (seems they don't know). If I need to replace this then which one is it.

Anyone come across a vacumn line diagram for the 4.3 W I may have a vacumn problem and not sure if the lines are their or correct?

Seem there are 4 according to info on AutoZone if they are referring to my engine which is a 4.3 W. They don't have that designation.

On my 98 safari it has 4 o2 sensor .