I know this wouldn’t happen with the Exec 2.x binding. It has been so long since I’ve looked at the 1.x version of the binding that I have no idea if that is how it has always behaved. It is not behaving correctly. The docs for the 1.x version imply that it should only execute the script on a command. But at this point, I doubt this will be fixed in the binding. You will need to adopt Alpoy’s suggestion or move to the 2.x verison of the binding.
On a side note, this Rule has a really strong chance of killing your Rules by using up all the runtime threads. You can only have 5 Rules run at the same time. If I read this correctly, this Rule runs at a minimum every five minutes. Then you sleep for ten seconds and then make a call to a script that can run for up to five minutes. And the Rule can itself change VolvoHeater, VolvoEngine, and VolvoLock causing the Rule to run again. In a worst case scenario you can end up with three or four of your Rules threads tied up for five minutes at a time.
See Why have my Rules stopped running? Why Thread::sleep is a bad idea for a detailed explanation and alternative approaches.