1994 Lincoln Mark VIII EGR Codes 558 and 332

I have a 1994 Lincoln Mark VIII that is feeding me a fault code of 558 (key on) and 332 (engine running). 558 means "EGR Vacuum Regulator circuit failure" and 332 means "Insufficient EGR flow". I tested the voltage at the EGR Solenoid and it's about 10 volts. I replaced the EGR solenoid but the same codes appear. Could I have a bad PCM? Also, the car runs smoothly however, the check engine light comes on periodically (it's not always on). If I get a code 558 with the engine not even running, doesn't that mean that the problem is electrical?

Please help! Thank you!! Randy