For example, the Toyota Technical Service Bulletin (TSB) EG045 - 07 for the 2003 - 08 Toyota Corolla and Matrix with the 1ZZ — FE engine mentions a leaking intake manifold gaskets in subfreezing temperature as a possible reason for the code P0171 along with some other codes. (samarins.com)
HR16 is equipped with intake manifold with long runners, what improves low - and mid-range torque. (mywikimotors.com)
It will be very good if you make port and polish for heads and remove TGV valves in intake manifold. (mywikimotors.com)