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here is the deal with stalling due to atmospheric bypass
1. first thing i do is make sure its actually the bypass. block it with some tape and a sock or something and make sure the stalling symptoms disappear.
2. If it still stalls with a blocked bypass, do a boost leak test.
3. if the boost leak test reveals no leaks, and the bypass is blocked but the engine stalls, there is a high chance the problem is the MAF SENSOR PLACEMENT. It is either too close to the turbo, or does not have the required bends. The compressor wheel on a non-bypass car ( when the bypass is shut at or near idle speeds) can surge silently (where you can't even hear it near idle) and this causes air to buffet the maf hotwire. Factory bypass valves hang open at idle to prevent this. You can alleviate (confirm diagnosis) this symptom by creating a boost leak down stream somewhere (pull a vacuum line off the intercooler plumbing, BEFORE the engine, so the compressor-airflow leaks). Air will leak out, preventing the compressor from surging and the engine from stalling as long as the leak is not large enough to run the engine too rich.
4. If the bypass is confirmed leaking-causing the stall, you have two options. First one is recirculate it, easy and cheap highly recommended.
Second option is to wire in a SAFC. They have a feature that will allow you cut fuel under circumstances to prevent stalling due to open atmosphere bypass.
Note
It is worth mentioning the factory computer (and PFC units) have a fuel cut for when throttle position is going to zero, which under normal circumstances (during shifts) cuts fuel just fine between gears, keeping the engine from running rich and stalling. It is only at low rpms (below fuel cut RPM allowable) that the factory computer can't cut fuel and that is where stalling typically persists. The SAFC function I mentioned simply extends this fuel cut to below the factory's set limit.
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