I'm getting random lean backfires when reving the car from idle (car idles at around 1500 rpm in neutral while coasting at times then settles down but that's a different issue) I can watch the O2's drop down in the low 60 to 90 mV when this happens. I just installed 1.6 RR's. I also have:
30lb SVO injectors (used Christian's SVO offset)
Headers
NOS 58mm TB (for dry setup)
3000 rpm stall

Other than that it's a stock iron head Impala SS.

I have new O2's sitting in the trunk - I've not changed them and car has over 100K - don't know if previous owner ever changed them.

Also have to slot the TPS sensor so full throttle doesn't throw car into limp home mode so it's .20V at idle

I can email someone my file if they wish to check it out.

Please help!
Mike

 

Did you miss a vacuum line? Just a change of rockers shouldn't cause this. Sounds like a unmetered air leak.

 

Well, it doesn't matter now...
Blew my 4L60E last night on a nitrous pass.
Car is now at the shop for ported/polished aluminum heads and 224/236 - 114 LSA Comp Cams LT1 Xtreme nitrous cam along with a new tranny and transgo shift kit.

Mike