One thing for sure, if someone claims to be a plain-clothes police stops you, you have every right not to entertain.
The rule of thumb in Malaysia is that, if you are halted by the police whether if you are driving or not, you get the sense of fear.
It is as if you have committed an offence but not knowing what it is. According to the law, you are under NO OBLIGATION to answer any questions or follow any orders from anyone claiming to be plain-clothes police.
This is because a policeman who is not wearing his uniform does not have any authority AT ALL.
When driving, if you are stopped by uniformed police officers, you should be aware of the following:
There should be nothing more than that
Only if you are UNDER ARREST that you should follow the police to the police station. If you are NOT, you have every right to leave.
If the police comes to you house, you have EVERY RIGHT to check their IDs.
Never allow anyone in without checking first. Get their IDs, jot them down and call the nearest police station to confirm that they have sent police officers to your home.
To enter your home, they need a search warrant. Unless you called for help, you do not need to let them in.
Unless you are under arrest, you need not have to follow them anywhere.
Again, plain clothes police do not have authority to do anything so, call for help if they try anything.