Mine had problems with idle also... I adjusted fuel pressure, fuel mapping (with piggyback fuel computer and wideband o2 sensor), and had the downpipe welded to the rest of the exhaust and it hasn't given me an issue yet. Thats the best answer I can give you with the info you put out. Do you know your air fuel ratio? Is your boost guage reading vaccum? Do you know your fuel pressure? Did you replace the fuel pump? You were talking about a resistor box, did you buy low impedance injectors? Need more info...