Very low oven flame

Ignitor work and oven burner will come on after 3 minutes and the flame looks normal. After a few minutes the flame goes very low causing the oven not to reach temp. This is an intermittent problem, surface burners work fine and the broilier seems to be ok. Do you think the problem is the gas valve #AP4098213 or the presure regulator #AP378185

Replace the oven ignitor. Tom