I would expect an accuracy in the neighborhood of +/- .5 to 1". I would wire it back up correctly, put a hose on the end and suck on it and observe the reading. If it shows 29" at a steady state and while drawing a vacuum, there is a pretty good chance that the sensor is defective. The fact that you get a 29" reading now, indicates no issues with wiring or the G3X. The inaccuracy should scale, so I would expect that a change in abient pressure of .4 would show at least a change of .3.
If accuracy is important to you, you can build a custom map in the G3X based upon actual, observed output from the sensor. That is what I did, as I used a GM sensor and the G3X doesn't have a table for that.
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 11-26-2020 at 08:49 AM.