I have been experiencing leanness (12:1-13:1) which has been difficult to tune out.
It occurs when my MBC spikes. The spike lasts about a quarter second going from 14psi up to 25psi before settling down to around 21psi. Yes, boost builds that quickly.
The injector duty cycle indicates that I still have plenty of fuel left and despite richening up that row I am still seeing leaner AFRs than I should.
My map signal line is pretty long- about 15 feet or so. It is routed through a grommet on the driver's side of the firewall.
I suspect that the long signal line length results in MAP latency, just enough so that my ECU's MAP sensor is a step behind fast transitions like the boost spike.
I have experienced similar vacuum/boost "lag" before. When I sourced my MBC signal from my coldside IC pipe, my turbo spooled about 400RPM later.
I think that I will try running a short line through the passenger's firewall. Maybe one of the holes from the now-removed A/C. Another "fix" would be to drill out my MBC restrictor.
I searched the web about this and it's funny, the only thread that came up was a four year old thread from this site: Length of MAP line?