MSP sputters and dies at idle

[Boilermaker19]

A few days ago, my MSP started having a problem at idle. When I first start it cold, she starts up okay, but once she's warm enough for the IACV to let the idle drop to normal, the car sputters and dies. I can drive it, but I sometimes have to rev it to keep it running at a lght. Once I am above 1500 RPM, everything seems fine. The Fuel trim readings are WAY negative, like -25, when she starts sputtering. The only codes are P0140 and P0037, both of which I have had since I bought the car in October. I have cleaned the MAF, shot some cleaner in the TB, and then I seafoamed her and replaced the plugs. After that, I cleaned both O2 sensors (which, BTW, are both giving a constant signal). I checked all of the vacuum lines, and they seem okay. When I ran hte seafoam, I got a lot of smoke coming from the region of the S pipe, which I recently had to have welded, but if my O2 sensor signal is constant, that can't be the problem. I am running 9 pounds boost (forged internals), an FMIC with BOV, MAF is blow-through, 12" from the throttle body, have a 3" catless exhaust and SSAFC.

[Code Monkey]

Constant = no change? Is your AFR fluctuating or is it stuck at one value?

[Boilermaker19]

The AFR fluctuates

[ihasmazda]

vacuum leak. check hoses.

[HFDSpace-Junk]

^^^ I second that.

other than that, check the plug wires and coil packs. I doubt that's the problem as it really seems like a vacuum issue, but cant be too safe. and lastly, check to see that the pump is working correctly and the pickup isn't clogged.

[Illa Noize]

Make sure the spark plugs are gapped correctly. Also make sure ur coilpacks are working correctly and also make sure the wiring connecting to the coilpacks have a solid connection. Mine weren't and I had to glue the wires to the coilpack so the connection remains good.