Just recently Myself and a Relative [Nephew] replaced his seized LXF for a s/hand LXF from a Wreckers,
After taking our time to install it, and re-installing the loom,
and Double checked the loom to make sure all the plugs were secure,
replaced the oil filter, topped it with oil & water.
Fired it up, and it run like a dog for about 5 minutes,
But we just let it idle in that time, and then its started running as smooth as silk after it had warmed up,
He did have a MIL on, but after a drive around the block, its had extinguished itself,
I was going to see what the fault was in the history, but got to busy cleaning after a 2 day project.
7am Saturday out with the old seized motor, and in with the replacement by later that afternoon 6pm
8am Sunday wrapped the loom the engine, plugged it all in, and installed the fluids, fired up at 1pm.
The worst part was removing the torque converter from the seized engine.
Him on the crank shaft bolt with a breaker bar and an extension handle,
and me with a bloody big screw driver on the ring gear, turning [forcing] the crank around,
so I can get the torque converter bolts at the starter motor opening to be able to remove them.
Getting back on the subject,
Its best to get it scanned properly, and then you know the correct codes that need to be investigated.