[btwilson86]

I don't have an answer for your hg question, but running a blow off valve (vented to atmosphere, not recirculated) can cause your engine to stumble and/or die when shifting. This happens because all of that air passed through the AFM, so the ecu expects the air that was just dumped to still be in the intake. The ecu then provides the amount of fuel to the engine needed for the volume of air it thinks is still there, causing it to run excessively rich.

You can eliminate this problem by running a bypass valve instead of a blow off valve (easy) or by running a system like MATT-PRO 2 (?) in speed-density mode (not exactly sure if that's correct; in any case this would be a better setup because you can eliminate the AFM, but my understanding is that it's incredibly difficult to set up). A search on the forum or Google should bring up several results for this particular problem, as it's very common