Symptoms indicates a faulty/stuck VSV and here are the testing procedures.
EGR VACUUM SWITCHING VALVE (VSV)
1. Disconnect electrical connector from EGR VSV. Using ohmmeter, check that continuity exists between electrical terminals on EGR VSV and that resistance is 33-39 Ohms @ 68 F (20 C). Replace EGR VSV if no continuity exists or resistance is not within specification.
2. Ensure no continuity exists between each electrical terminal and the body of EGR VSV. Replace EGR VSV if continuity exists between electrical terminal and the body of EGR VSV.
3. Apply air pressure to port "E" without battery connected. See
Fig. 20. Air pressure should flow from port "G" at end of EGR VSV. Apply battery voltage and ground to electrical terminals on EGR VSV. See Fig. 20. Apply air pressure to port "E". Air pressure should
now flow through the air filter. Replace EGR VSV if defective.