A few weeks ago I had broken the hard vacuum line running from the EVAP solenoid to the throttle body on my wifes impala. To make it better for her, and to keep me from sleeping on the couch, I took that line from my car and put it on hers. I plugged the appropriate spots for vacuum control, or at least I thought I did.
Shortly after this, I developed a stumble on acceleration and a flashing CEL. I scanned the codes and found a #2 cylinder misfire. I did some trouble shooting, replaced the plugs, and test drove it. Stumble got worse, and I was at my end when it suddenly hit me. The fuel pressure regulator is attatched to the same vacuum port. If the other EVAP port is not sealed correctly the fuel pressure regulator will not get the proper amount of vacuum and cause the car to run rich. I tried a different method of sealing that part of the vacuum port. The low end stumble is gone, though the hard acceleration stumble is there. I am pretty sure it will go away when I get the replacement hard tube line.
I just wanted to let everyone know that a small vacuum leak close to the FPR will cause problems.