1994 Nissan Pathfinder cold start

I have recently purchased 94 nissan pathfinder from local auction. Really got a good deal on it, did basic tune up drove arond for about 2 to 3 oil changes when all of a sudden check engine light came on. scanned obd1 system and it read egr malfunction and knock sensor malfunction. tested egr and tested good did notice that vacum was lacking so replaced vacum module and still have no vacum or movement out of egr. I also replaced temp sensor for egr cant figure out whats going on please help!