1990 200 missing/lean under boost

[David M. Yentema]

This is an issue i've been dealing with for a while, Car is a 90 200 Quattro, MC-2, Ben Swann 2+T super chip (mac-14)

basically what it's doing, it idles fine, starts up fine most of the time (accumulator was leaking, so I pulled it, made no real difference with starts, still vapour locks, but that's besides the point) and it will pull to about 6psi, but the second it goes over that, my NB shows full lean, and if I push a little further you can feel it miss slightly. I know a miss will show lean, and that actually running lean will show lean.

I have tested and verified:
ISV, IAT, Idle/WOT switch, ignition coil, cap, rotor, wires ohm out fine but they're old so I plan on replacing them anyway, pressure tested the intake manifold and fixed the few small leaks I found.


I also bought an adjustable spark gap tester, adjusted it to the absolute max distance the coil would jump, and tested each of the wires, all of which were able to jump the gap no problem


I'm running out of ideas here, and there are no codes being set. The only other idea I have is to tape off the intake snorkle and run pressure into the whole intake and see if anything is leaking (thinking being a vac leak before the turbo, but after the metering plate would cause a lean condition, especially as the turbo spools and sucks in more air..

any suggestions you guys can give would be awesome

Thanks,
Dave