Question re: Mazda Protege 5, 5 speed manual non turbo. The issue - car is stalling/chugging when idle-ing at stop signs/red lights/stop go traffic. I have replaced the EGR valve, spark plugs, spark plug wires, ignition coils, air filter and the O2 sensors were changed about a year ago. The last fix I tried was the spark plugs and iginition coils - car ran great for a month after the change (check engine light was still on, code p0421). It just started acting up again, chugging but not to the point it dies.