1998 Bonneville P0122 error Code

I have 1998 Pontiac Bonneville with 141,000 miles. About four years ago, the engine (3.8liter) was replaced at 96,000 miles when coolant got into the cyclinder #2 and destroyed the engine. Two weeks ago, I had a small coolant leak and suspected the intake manifold and had it replaced. The check engine light came on and has been on ever since the intake manifold was replaced. I changed the throttle position sensor this last weekend and reset the error message. Error code P0122 came back on after one day. What else would you recommend I try to remove the check engine light and this error code. Thanks in advance