2002 Mazda Protege emmision issues

So first my car started chugging really bad at idle and first starting off. It was fine when it got up to speed. So we changed the spark plugs and wires. That did it for 2 weeks and it started doing it again only this time heavy white smoke comes out the exhaust pipe. And back to chugging again. Changed the mass air flow sensor both o2 sensors and all fuel injectors. After the injector replacement it has improved on the chugging aspect but it still chuggs just not as bad. Still smoking. No cadalitic conveter don't know what else to do.