Hi
I don't have many mods (well cat back zorst and pod) and I noticed mine having a bit of a lumpy "pop" noise in the zorst at idle which wasn't so noticable during driving but no doubt still there. I went thru what you're experiencing. Turns out my injector in cyl 6 wasn't closing off and had overfueled the cyclinder and washed all the oil away from my valves, significantly dropping my compression in that cyclinder.
Long story short, do the following:
1) Clean out your AFM, you'd be surprised how much cr*p gets built up in that little item.
2) Clean out your injectors - probably can't do this yourself? Find someone that can.
3) Get new sparkies if necessary. I haven't gapped mine but as I said, i'm pretty standard.
4) Get someone to perform a compression test on your cylinders.
Other than that, I can't help :headspin:
Cheers!