My 3 year old KICKR suddenly died during a Zwift race last Sunday. I bought a Tacx Neo 2T. I did the Tim O’Donnell ride this morning and the TACX felt great. And then I tried to do the FTP test in ERG mode. I quickly noticed that ERG mode wasn’t working. The workout said ride at 150 watts and I could ride at 50 watts, 200 watts, etc… ERG wasn’t engaging. I downloaded the newest software. I made sure the ERG toggle was on. Nothing helped. I spent an hour on the phone with a useless operator at Garmin. I finally talked to a helpful technician at Garmin. He told me that they could send me a replacement unit in November or December. Anybody experience a similar problem? Is there an easy fix that I am missing? I have heard that ERG mode on TACX is shaky, but this is absurd for a $1400 Trainer.
You spoke with Garmin, so perhaps you already went through all this with them—but can you say more about your setup? Are you using Apple TV, Mac OS, PC, tablet, phone? And how are you connecting? Ant+FEC, BT ?
I’m on a Neo 2T via ATV4k (BT) and have never had any issues at all with ERG mode.
Zwift. PC. Ant+.
Are you using the FE-C option?
@David_Rippon_Dirt You posted again about your issue with ERG mode 5 hrs ago in another thread, but you didn’t reply here—are you using the FE-C option? Is your Ant+ cable close close close to the Neo? Could you even just as a trial run connect the Neo via BT to test ERG that way? There are a lot of people using Neos… so, while it’s possible that you got a wonky unit, it’s more likely that there’s some issue with the setup; let’s get you a solution.
I have another theory. Is ERG mode on Neo different than ERG mode on KICKR? KICKR keeps you right on the wattage in the workout. Neo seems to allow you to be 20 or 30 watts above or below the goal wattage which is more like it should be. Maybe I just need to get used to a NEO trainer.
The Kickr isn’t keeping you on wattage any more than the Neo. Our pedal stroke isn’t perfectly smooth; i.e. we apply more force here, less there, etc, and it changes with every stroke to some degree. For the Kickr to “keep you on the wattage” (i.e. not allow any fluctuations) would require it to increase and decrease resistance instaneously many many times per pedal stroke regardless of any BT or Ant+ lag. If there is a significant difference in the wattage between the Kickr and Neo, it’s more likely in what is being displayed on screen. To that end, do you have the trainer (in-game, in settings) set to instaneous or to 3-second average power display? It makes a big difference in terms of the power figure you see displayed and how consistent it is—but it wouldn’t change the issue, the feeling that ERG isn’t holding you to a steady wattage.
But you still didn’t answer the previous questions.
Same result with BT and Ant+. Using FE/C. Everything same in set-up as it was with my KICKR.
To the point Xavier made above, what you saw with the Kickr was just related to how it communicated power to Zwift. The Neo isn’t ‘allowing’ +/- 20-30 watts, that’s just how your power output is changing and the Neo is trying to constantly adjust to what the workout wants. The Kickr just wasn’t showing you that this was happening. It may just take a little getting used to, but try to just be constant for each interval, as opposed to trying to adjust to the power you see in the screen, and I think you’ll find that you stay much closer to the requested wattage.
Thank You. 
@David_Rippon_Dirt Everything Nigel said is good and to the point, but it can’t explain your original post where you said you could fluctuate from 50 to 200 watts, to say nothing of your post in another thread where you said you could fluctuate from I believe 50 to 300 watts. ERG isn’t going to give you a 150-250w free fluctuation range. So if you really were able to fluctuate between 50 and 200-300 watts when you should have been in ERG mode, we haven’t solved the issue.