I did a lot of searching and got some good advice when I had audible ping not too long ago. Here is a list of possibilities pasted from my thread. Engine managment would be a very good consideration for you and you could do some logs, they might help.
Results from searches:
1)Cobb map is conservative, runs rich. Should be trusted.
or (take your pick on the thread)
Cobb map is actually leaner than stock - never heard of anyone running Cali 91 map on 93 octane, but is a possibility.
2) PCV valve - should be changed every 15K miles, or never (take your pick). Mine was fine.
2.a) Oil catch can - not done.
3) Turbo oil seals shot - seems not. No oil in downpipe, not much in intercooler
4) Engine deposits - can cause preignition as well, or increase compression and otherwise cause spark knock (at issue here). Finishing 1st tank with synpower cleaner.
5) Spark plugs - do show signs of detonation (metal balls stuck to ceter electrode). Plugs replaced with OEM gapped to .028 (yesterday, not tested hard yet).
6) Blow by - oil in intake, reduces octane. Check compression.
7) Elevation - Colorado people say 91 octane = 93 octane there, should be a safeguard
Need higher octane at high elevation (web auto professionals and occasional threads)
8) Boost - peaks at 15.8 settles at 15 then tapers. Compensation map in ECU reduces peak boost by 1 PSI per ~3500' IIRC, so normal stage II numbers.
9) Vacuum issues (haven't figured out how to check system yet).
10) Injectors plugged, tired, or imbalanced (40K miles, always top tier gas, never cleaned). Unlikely - all four cylinders are affected.
11) MAF or Temp sensor problem.
12) Dealer - go parade my just installed stage II setup and void my warranty on a totally unabused motor with a potentially bad ring land. Get unheard of and unreported "ping" reflash that was never mentioned when I was there complaining about ping.
13) Knock Sensor? Don't know how to test that.
14) Head gasket??? I guess I should add this because I have had to burp the coolant a few times recently. I had a small coolant leak from a line a while back but it was supposedly corrected/pressure tested at the dealer. The system was then flushed at 30K (dealer) and there has never been any indication of overheating.
i think getting this re-flash may help...but i'll def go down your list tomorrow when i have the car apart.