Wow. I suppose it depends on who is tuning. Some people thing they are clairvoyant or something (with a car...
) and some people claim they need everything.
-throttle position absolute
-rpm
-maf AD counts
-airflow in #/min
-load
-open loop flag
-imrc state (if imrc involved)
-Long term fuel trim bank 1
-long term fuel trim bank 2
-Short term fuel trim bank 1
-short term fuel trim bank 2
-O2 sensor bank 1 forward (or upstream)
-O2 sensor bank 2 upstream
-coolant temp
-intake charge temp
-spark timing
-knock sensor retard
This is probably the basic list and covers most requests. There will be specific requests if an issue is detected.