Almost all of the cars here have it. Differnt intakes, no intakes, some with exhaust, some with headers, some with AFC. It does not seem to matter what parts you put on the car. Some mods definitly do make the problem worse though. Intakes for one.
I noticed on a dyno chat posted about AFC's that there was a pretty serious dip in AFR at ~4000 rpm. From looking at the dyno charts posted you could see a drop in HP and torque inline with this change in AFR. Could this be a ECU "defect?" Does anyone know if there are any high versus low rpm vacumn switches? Some sort of Emissions thing that helps kill high rpm polution? or vice versa. If the knock sensor thing works for you Mark, I will have to have a knock sensor day here.