In taking my 1978 Z28 Camaro in for its biannual smog certification I found out that it failed because the EGR valve was non-operable. I read some past threads on here regarding EGR valves which were very helpful in explaining what an EGR valve does, how it works, etc. I am still confused though on exactly which EGR valve I need to replace my old bad one. As mentioned my car is a 1978 Z28 with auto trans and California emissions. Is the correct EGR valve for my car a positive or negative back pressure one? Is 17052714 the correct part number? Does it really matter which EGR valve I use as long as it fits and operates? Thanks guys for your input.