O2 sensor going "offline" for a brief second and causing tuning issues

[Jack@European_Parts]

It may be fuel enrichment is popping the ECU into Open Loop; and when in OL *may* not report sensor voltages - although I don't know enough about your particular ECU or what a tuner may have done. Bottom line, if the MVB from the ECU looks to be deceiving you - do a direct measurement.

Connect a multimeter to the O[SUB]2[/SUB] sensor by backprobing the plug coupler; run the leads into the passenger compartment and have a second person reading the meter. Do this for both the reference voltage and the sensor output voltage of the O[SUB]2[/SUB] sensor.​

Holy shit a common sense approach what do you know OP right, do you know how to use a meter and measure amplitude with a scope?

Know what I like about mechanical and electronic & externally tested components, is it is to catch the FOD! and whether OEM or leave it alone tuning process & doesn't pass the what was Jef saying, the SNIFF test?

Are you using an external amplitude mixture gauge to watch and match to your ECU logs like all the racer nuts?

 

[Jack@European_Parts]

Sounds like someone needs some design and theory education huh?

http://www.vaglinks.com/vaglinks_com/Docs/SSP/VWUSA.COM_SSP_941003_Audi_Engine_Management.pdf