Car backfires between shifts.

I installed a large NPR front mount a while ago and now my car doesn't seem to be running quite right. When i am driving casually and shifting at around 2500-3000 rpm the car lets out 2 backfires between each shift (pop pop), this is a little embarrassing and very annoying. If i shift earlier it doesn't backfire, but i am way out of the powerband and the car feels boggy, if i stand on it the car runs fine and doesn't backfire either. It only backfires if i am driving casually and shifting between 2500-3000 rpm. Vacuum is good at about 18-19 inches at idle, i've been playing with the timing and it seems to be worse with the timing retarded to 10* so i advanced it back to about 14* with the spout out.

P.S. One day i took off the NPR tubing kit and put the stock intercooler back on and the car didn't backfire, when i reinstalled the NPR the problem came back.

Anyone know what's going on here?

Since you mentioned that it went away with the stock intercooler on it...we should assume that it is related to the mod. Typically when an engine backfires through the exhaust on decelleration, it means that it is running lean or has an exhaust leak at or near the manifold. If the problem went away with the stock cooler back on it, the only thing that I can come up with is that it is now somehow lean. Anyone else explain why this might be?

Cooler air is more dense.... therefore more air molecules, would make it run leaner if not adjusted for more fuel or maxed out with the stock setup. However i would think driving on a cold day stock IC would be cooler than a summer day with a better intercooler... im sure someone will have some better ideas.

1.Are you running a BOV with the front mount?
2.How about with the stock IC?

Just guessing but if the answer to 1 = yes, then make sure you got it set up right, make sure it isn't leaking when the engine is in vacuum.

I am not running a BOV or BPV at this time, i have one but it's not installed. I also checked for exhaust leaks and found a small one where my 3" stinger downpipe meets the turbo, so i made some adjustments and got it to seal. It still backfires.

When i stand on it she goes rich and pulls okay (could maybe pull harded with a better tune). I don't have a wide band, i just have a cheapo autometer a/f gauge.

Also, if i don't let off the gas all the way when i'm shifting, it won't make that noise