Hi Markfe,
I had the same problem with my 3200, "slow down" message when I drove it harder (first the message is blinking and then stays on if I continue to push the car), and the error disappeared as soon as I stopped the acceleration.
The slow down message indicate that either:
1. One of your catalytic converter (or both) is too hot.
2. The thermocouples sending the temp to the specific ecu don't work properly.
Item 383300185

3. The ecu controlling the temp doesn't work properly.
Item 383300184
The first thing you need to do is to check the temps of your catalytic converters.
Easy with a gun thermometer (like this one,
https://www.amazon.co.uk/Non-contact-Th ... rds=ir+gun)
But in my case, the cat was so hot you didn't need a thermometer, after a spirited drive, it was glowing red

If one of your cat is hotter than the other, it means that a certain quantity of fuel is unburned in the engine and flow to the cat (increasing his temp by burning inside), check your spark plug, if one of them is full black, you've almost found your culprit, either the plug or the ignition coil. Not expensive.
If the temp of your catalytic converter is in an acceptable range, there is no danger but it means either the specific ecu or one of the thermocouples doesn't work anymore.
Hope it helps.