Backfiring on open throttle
 

Over the past few weeks, my car backfires every now and then when I open up the throttle wide. This happens maybe once a week, and only with the pedal to the floor.

I did a search of this BBS and found threads dealing with carbs (mine's FI) and threads dealing with backfiring on decel. I couldn't find anything about open throttle backfiring.

So I ask you, what might cause this?

Thanks in advance,

two things to look for are a leaking cold start valve if the backfire is through the intake. and exhaust leaks if it is out the tailpipe. Also maybe the MPS could be doing it?