The PO251 code is almost the death code for the IP. >>
Engine running, then the PCM detected eight (8) consecutive Camshaft signals were missing, or that an average of eight (8) Camshaft signals were missing for 32 No 1 Cylinder events.
So your encoder (Optic Sensor) is not picking out signals from the disc in the IP. So what do you do? First make sure there is no "Electronic Filter" plugged into the encoder. Next make sure no air or dirty fuel is entering the IP. Third make sure they Installed a new encoder in the IP.
Fix might be a new encoder or a new IP
And your timing chain should be replaced around 150K for best performance.