Part no for the MAP sensor on 07 WRX Hawkeye

Well, that sounds expensive, but I hope for the best.

Is there an actual CEL code thrown for the MAP or did you just decide to try it unplugged? Because the function of it does not affect the symptoms you're having. And yes, that is very basically what the boost control solenoid does. When pressure builds up under boost, it goes through a line with a restrictor pill into the BCS, then from there to the wastegate actuator. So without it the pressure will build up until the pressure going through the line equals the wastegate spring and opens the wastegate, so you can't build any more boost than spring pressure without the BCS reducing the pressure in the line. None of that ties in with fueling though.

I'm speculating that your issue is during closed loop fueling. When the car is warming up, it is in open loop and just using the maps in the ECU basically and the MAF signal. When it warms up it uses closed loop for feedback bringing in the reading from the front O2 sensor and adjusting fueling based on that. This is used in non-WOT conditions, as in idle and decel as you described - it kicks over to open loop for higher load/RPM conditions. The only relevance of the MAP I can even guess of is maybe it kicks you out of closed loop when it is unplugged. The sensors that are needing to be checked IMO are the MAF and the front O2, unless you're seeing a CEL for the MAP. Cleaning the MAF is about 10 min. total and MAF cleaner is cheap. You can unplug the front O2 to force it into open loop. You will get a CEL and a rough idle but it should run without it if the O2 is the only issue. Mine is waiting for the new front O2 on Sat and has been driving OK without it for a few days. They only last ~100K miles. Also you may want to look at the idle air control valve.

For the P0108 you need to diagnose it is either the sensor or supposedly an air leak will cause it. I'm guessing the latter, which would not be helping it run properly either. I'm not sure where it would isolate to, but I would check everything from the MAF (check for common tears where the inlet seats on the turbo), vacuum lines (especially those involving the BCS per the other code), intercooler hoses and gaskets on the underside, BPV itself and gaskets there. This doesn't really make sense to me, but is what people have reported working.

For the P0244 I don't think that is a BCS failure code, it is an overboost code. So, you have a leak in those lines, or you have boost creep possibly if you have no cats.

These lines are the ones that matter for that (except the one going from the BCS to the intake is less important). If pressure leaks out here it won't open the wastegate, or not as much as it should. Also the restrictor pill is required, don't lose it and make sure it is there. The T and the lines must be the correct ID too if replacing.


Edit - also it seems to me that the MAP reading excessively could be a result of overboosting as well. It makes sense to me but I haven't heard of it directly.