TMCC shutdown erractic

I've had a similar experience with 3 different TMCC + RS2/RS5 locos/trains (NOT Legacy) I run on my layout:

• Lionel Amtrak Dash-9 #510 w/ERR CC-M upgrade (single loco)
• Lionel UP GP-9 Lash-up #2380 & #2381 + additional UP GP-9 #2397 (train)
• K-Line Rio Grande F7 A-B-A (single loco - dummy B-unit & trailing powered A-unit are slaved to the leading A-unit)

However in my case I don't think it can be attributed to the antenna b/c all other commands (sound, speed & direction control, smoke/lights on/off, etc) all work perfectly for these locos/trains regardless of where they are on my layout. In addition, all my Legacy and LC+2.0 locos/trains shut down perfectly every time. I'm curious if anyone has other theories or explanations for this.

On some of my TMCC engines I have to manually lower the RPMs and then shut down works.

All other features on engine with the shut down problem also work fine anywhere on my layout. Regardless if I lower the rpms or not, shut down erractic, sometimes works, sometimes not.   I was just assuming it was the antenna placement,   Why does it work 100% with shell off engine, laying beside engine????    Is antenna placement being interfered by some electrical devise when shell on engine????     Someone must have the answer.

@MartyE posted:

On some of my TMCC engines I have to manually lower the RPMs and then shut down works.

Good thought @MartyE. I am aware of this requirement and do lower RPMs first. I don't think that's the issue, at least not for me.

If the round thing in the top of the shell is a speaker. Maybe try moving the antenna away from it. Don't know it might help.

That TMCC behavior, requiring you to bring the diesel to idle run level before shut down, was by design. Neil thought that that was more of an intentional or realistic behavior. Since the user was manually initiating a shut down sequence, why not play along and require that they would run it down manually to idle first. If there was a battery installed, and track power was removed, then a natural sounding shut down would happen automatically.

I agree with Neil.