I am not an expert but i don't think it could cause any idle problems. The DPFE tells the computer how much EGR flow there is so it can adjust the amount of vacuum applied to the EGR valve thereby opening or closing it more/less. However, at idel the EGR valve should be fully closed reguardless. If the DPFE senses flow at idle i would 'think" this would cause some sort of fault code to be generated. I had a intermittent rough idle problem and it turned out to be a bad IAC (Idle Air Control) valve. The acutuator would stick, I probably could have cleaned it but i just put on new one. Don't know if this is your problem but you could check it.