I have an 85 Bronco 5.0 EFI. It starts right up and runs fine until it's all the way warmed up. Then, the idle will go above normal and drop below normal starting gradually then ending in dying on the low side. When warmed up, it will still start right up and rev over normal but die as the idle drops. It last had a code 31 EGR/EVP. EGR moves and holds vacuum steady and EVP is new and within spec.