A quick copy and paste from a document I wrote for someone a while ago. On a new R90E from TT, you'll probably find that you'll need to wind the lower of the two screws out quite a way to get it operating as it should. Confused me for a while when I changed the one on my P38 as the old ones were almost fit and forget.
Setting up a Leonardo
Software is simple enough to get things going. Plug it in and start her up. On the main screen you'll see things like the lambda output and actuator opening. To start from scratch you ideally need a manual valve to fit in place of the actuator. If you don't have one, I've made one using a plastic water pipe Tee piece and a seat belt mounting bolt but you can use just a length of hose and squeeze it with Mole grips if you have nothing suitable.
Take the stepper actuator out of the hose and fit the manual valve but leave the stepper attached to it's cables so you can see what it is doing. Set the manual valve about half open. Go into the software and under the Actuator tab (under Optional Configurations), set the upper and lower limits to 255 for idle and out of idle. If you make any changes in the software you must hit Return after typing the new value in or it doesn't save the setting and reverts back to what it was. Also make sure the actuator default lock box isn't ticked. Screw the idle bleed screw, the top one, all the way in. With the computer connected so you can see what is happening, start the engine and get it running at around 2,500 rpm (screw the throttle cable out on it's adjuster if you are on your own). Adjust the manual valve for highest revs (and adjust the throttle to keep it the same) and check the opening on the stepper. It wants to correspond with what you have the manual valve set at and, looking at the software display (hit F12 to display what is going on), you'll see the lambda sitting either somewhere in the middle of the scale or flipping between extremes. You want the actuator and the manual valve to be somewhere in the middle, around 120 - 150 on the software display. If it is right at the top (fully open), you need to unscrew the main bias screw on the vaporiser half a turn (the lower one with the spring under it) at a time until it is in the middle somewhere. Too low (fully closed), screw it in. Re-tweak the manual valve to get the revs back up. Keep doing this until it is sitting somewhere in the middle. You can check that the actuator is working by watching what does when you adjust the manual valve. Screw the manual valve in a little to make the mixture weak and you will see the lambda go green and the stepper open up to try to compensate. Screw it out to make it rich and the lambda will go red and it should start to close.
Now remove the manual valve and throw it somewhere, you may need it one day but hopefully not for quite a while, and fit the stepper in its place. Start the engine and hold the revs up to confirm that it is still in the wandering around the middle and the lambda output is flipping from one extreme to the other. Let it drop to idle and see what the stepper sits at then. It wants to be roughly the same at idle as at 2,500 rpm. If it closes down, screw the main bias screw in a touch to bring it back up. Rev it again and check that the stepper is still in roughly the same area. You'll need to try this a bit to get the idle and out of idle opening the same. You won't be able to get it spot on and a slightly higher opening at idle is fine. If it opens up at idle, then try screwing the main bias screw out a touch. If you find you can never get the out of idle opening within a sensible range and the idle is still opening up, then open the idle bleed screw a touch. I do mean a touch, it is very sensitive, especially on the newer ones with two 6 mm adjusters.
Finally, when you are happy that it is as good as you are going to get, close the actuator limits down to something sensible, say +-30 at idle and +- 40 at out of idle. If you are lucky, you should be able to get it looking like this https://www.youtube.com/watch?v=b6sGp2I9lts
which is my 4.0 litre on an identical system.
If the lambda sensor is dead the Leonardo will be adjusting the mixture using incorrect information so getting it wrong. The 0-1V Zirconia sensors used in a 14CUX Classic give 0V for a lean mixture and 1V for rich. So if the lambda sensor has died it is giving 0V, the Leo sees this as a weak mixture so will open the stepper up to make it richer. That will cause you a problem..... In this case, using your manual valve, get the vaporiser set as above and note the actuator number. Tick the Default Lock box and type that number into the box that appears next to it. Then set the idle and out of idle steps to +-5. That way you will have locked the actuator opening to that fixed opening where the mixture is as close as it is going to be for most of the time. Then when you have replaced the lambda sensor, you can set it up correctly.