Headache
 

I have a 2000 pontiac bonneville SSEI, that has 167,000 miles. Today I had it checked for service engine light codes. The codes were P0300 and P0405. The car runs rough and lean. The EGR valve has been replaced 2 times in the last 3.5 years. What could be the cause of my codes? What should I check 1st? Does anyone have a clue? Could it be the fuel pressure regulator? **random misfires too**:confused:

Moved to proper area.

The P0300 is a random misfire.

The P0405 is here. https://www.gmforum.com/obd-ii-trouble-shooting-153/p0405-285077/ There is a much of tests you can do.