Timing Situation

[stash420sx]

I was running some tests on my car for school and when checking my timing I found that it retards itself everytime I open the throttle, especially from idle. The scan tool I was using showed my timing dropping as low as -5. My timing shows 20 btdc at idle, and the same with the TPS sensor disconnected. But I think the computer still adjusts the timing even with the TPS sensor disconnected. Which leads me to, how do I adjust the timing? All my sources say I have to use a nissan scan tool to enter set timing mode. I assume this program dissables the computers control over timing. The general consences on these boards seems to suggest all that is necassary is disconnecting the TPS sensor. Any thoughts or suggestions.

[Asleep Altima]

per the service manual, it says to disconnect the tps prior to starting the engine to check the timing. go here for complete instructions: Ignition timing how-to