I just did the same thing on my 1983. I had to replace it. It's called the Ported Vacuum Switch. The one for my 83 costed 83$. However, in my disbelief, I cross referenced the part with a 1980 and it was only 30$for the 1980 and functions exactly the same. The only difference was the shape of the housing.
Between 131 and 203 degrees, the vacuum advance is actuated, and the EGR valve is operational. During warm up the timing advance is closed and the EGR does not function in order to warm the catalyst. You could run the timing advance directly to the intake, but your idle speed would suffer during warm up. If you don't have emission testing in your area, you don't really need the EGR. Mine isn't hooked up because my car has a header and no catalyst.
http://www.autozone.com/autozone/parts/Duralast-Ported-Vacuum-Switch/1980-Nissan-Datsun-280ZX/_/N-im0lpZ93xpw?counter=2&filterByKeyWord=ported+vacuum+switch&fromString=search&itemIdentifier=68710_148373_0_
You can get all the free FSMs you want on Xenon.com. No need to buy it. Just type in the year and model and download it. http://www.xenons130.com/index.html