Help; Rough running Continental O-300D

I had the close to the same thing happen on a 172 with O300A. It turned out it
was one spark plug lead that was breaking down.

Idle and mag check was good. Static RPM check was was okay. However when
throttle up engine ran rough.

Replaced bad spark plug lead and everything waqs fine.

On another note, that engine runs 7:1 compression ratio and doesn't generate a
lot of heat (six cylinders - 145 hp). I found that if I did not lead
aggressively during taxi and ground use, the plugs would foul easily. Once I
started leaning aggressively, I never had anymore problems. It should be noted
that when I sold it it had 2600 hr on the bottom end and 1000 on the top.
Temps and compressions were great, the current owner, now flys theplane
regularly.

Just my take - check the leads and lean aggressivrely.

Larry