P0403 code

I can’t seem to solve this problem and it’s driving me crazy! I’ve read multiple threads on the same problem and I’ve tried all the suggestions, but nothing is fixing. I have a 2001 Mitsubishi Eclipse GT with 148,000 miles on it. About 5 months ago, the SES light came on and pulled a P0403 code. I replaced the solenoid valve and cleared the code and it never came back on. Then, about a month ago, the SES light came on again and is now pulling a P0401 code: “Exhaust gas recirculation flow insufficient detected.” I did not bother to change the solenoid valve again, as it stayed off when I replaced it after the P0403 code, but I did have the EGR valve replaced. After that did not fix the problem, I also had the entire system thoroughly cleaned. Even still, when vacuum is applied, the engine will not stall, although, the RPM’s drop. I figure if it was the solenoid valve again, it would throw the same code, and the ECU seems fine as there are no problems when the car is running. Aside from the obvious question as to what else this could be, if a solution cannot be found, is this something that can continue and not affect how the vehicle runs? In other words, is this mainly just an emissions problem, or is it something that is eventually going to make the vehicle inoperable? Thank you.