I have seen this issue several times before on the Vibe. The fix is to replace the PCM (powertrain control module) GM has published a technical service bulletin regarding this issue. I have included it below for your reference.
#PIP3621: DTCs P0171, P0441, and/or P2420 - Inspect Production Part Number on PCM - keywords CEL check ECM EVAP lamp lean light repeat trim updated - (Nov 9, 2005)
|Subject:||DTCs P0171, P0441, P0455 and/or P2420 - Inspect Production Part Number on PCM|
|with Automatic Transmission (RPO MU4) |
|and Base Front Wheel Drive (5th Digit of VIN = L) |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
On rare occasions, a check engine light may be experienced with DTC P0171, P0441, P0455, and/or P2420. These DTCs may be a result of an internal PCM driver issue that may keep the EVAP purge solenoid control circuit grounded at times instead of supplying a pulse width signal on the circuit.
If the SI diagnostics do not isolate a cause for the concern, inspect the white PCM label for any of the following part numbers, which may be causing the concern:
If any of the above part numbers are found, replace the PCM with the correct one listed below:
Auto FWD with RPO JL4
Auto FWD without RPO JL4