I'm having some interesting new issues with my MAF.
I decided to build my own intake plumbing between the turbo inlet and the MAF, and in an attempt to quiet down my intake, I've begun building an intake box to quiet things down and to also direct some cooler air into the engine. However, I'm learning that the SR20DET MAF is very sensitive to changes in the air flow.
At the moment, I've got a cheap adaptor to fit a K&N style filter onto the MAF. Based on my wideband O2 sensor, the engine runs very lean, to the point of sputtering out and dying at idle. It's a bit like when you have a leak in the intake. However, when I take the filter off and provide a little bit of restriction to the air flow going into the MAF, the idle smooths out and richens up a little. This makes me think that without this restriction, the flow of air past the MAF's hot wire doesn't go fast enough for the computer to figure out that there's a bunch of air going in. With the restriction, air flow speeds up across that wire and voila, things work out.
I've fiddled around with some sheet metal restrictors - a sheet with a bunch of holes in it (no good), a sheet with one small hole in the middle, smaller than the MAF intake port, but ported like a venturi (no good), and also a sheet with just a flat hole (better than the other two, but not perfect). Oddly, the BEST is just putting my fingers over the MAF and varying the spacing between my fingers until I can hear the idle smooth out.
All this makes me wonder if the stock air box has some engineered plumbing to address this very thing. I'm a little baffled by the two different size holes on the MAF: one is outer hole that you'd connect either to a filter or air box; the other is inner hole that much smaller in diameter, and located adjacent to the tiny hot-wire hole.
Any advice on this?
71 510 2-door SR20DET (S13)