I have had this issue for the past 3 weeks since buying this car from a used dealer. They were able to tell me what it was and lowered the price because of the constant check engine light staying on. It was a northern vehicle for so time by the under body rust but the cars integrity is fine but the exhaust was nearly gone. I have retained the original catalytic converter but replaced both O2 sensors, EGR valve and put a NEW exhaust manifold as it was cracked but the OBDII still reads Insufficant Recurculation Flow, Bank 1 O2 sensor, and EGR valve. Im thinking that the catalytic converter needs to be cut-off and replaced. PLEASE SOMEONE GIVE INPUT

 

Start with the EGR valve and replace it. Insufficient recirculation and O2 sensor codes could be secondary codes that are coming up because of a malfunctioning EGR

 

take off the egr valve and clean the ports inside the intake manifold

 

i have replaced the egr, o2 sensors, and fixed the header that was cracked