Starts just fine when double locked from the outside. As Dave
pointed out, if it is fitted with a factory alarm system (available in
87?) then things may change.

Are you sure the car will start?

Lock the doors using the KEY, then reach in through the window and try
starting it. In this condition, the car will think that it is locked, and
when locked it has no reason to start.

If you lock the doors using the door lock, AFTER the doors are closed, then
the car knows it is occupied and in this condition it will start.

You might be right that the early cars do not have ignition bypass, but my
money is on them having it. And, current cars will have it, I have no doubt
of this. However, the only way to test is to lock the doors from the outside
using the key, then simulate what would happen in the event of a theft
attempt -- the doors will remain locked but a window will be broken out, and
the ignition will be jacked so that the car  sees the ignition switch go on.
You create this scenario by lowering the window before locking the door,
then reaching inside (or climbing inside if you want) and using the key to
start the car.

Please keep in mind this is an 87 we're talking about here. Central
locking isn't tied into the ignition circuit at all in these older
models (not sure it is in the newer models either). My car (an 89
325i) will start reguardless of the locked condition of the doors. My
guess will be a fuse has gone out somewhere in the system. I'll find
my fuse table later and repost as to which one(s) I think it could be.

I do not know what you need to bypass the system.

But, if you locked the doors -- central locking system -- then managed to
get a door open, the central locking system still has control of the
ignition system, and it will prevent the car from starting. It this point,
the car thinks it is in the midst of being stolen, and it is protecting
itself.

I accidently locked the driver's side door and initiated the Central Locking
System.  Well, it took me a while to unlock the driver's side door again.
The passenger side is still locked and now the car won't start.  Question:
When the Central Locking System is engaged, will that shut down the entire
system, including starting the car?  I have at least the driver's side open,
but am surprised that the car won't start.  Secondly, what do I need to do to
disengage the whole system ... this is pain? Thanks for any response in
advance ... BMWFKK