Mystery Connector in Wiring...any Help? Blk/Wht in front of firewall (under plastic.

[AFARR]

I found a single wire locking connector (one end) while changing the blower motor out on my '91 318is today.   After pulling the motor out, and putting the wiring harness back under the cover, I found the other end.

It is a locking connector, and appears (wires are a bit dirty) to have a black/white stripped wire on either side of the connector.

I plugged it back together (now, I have been into the blower compartment repeatedly (checking the resistor, and swapping the motor), and don't recall if it was always unplugged or was plugged together.  

Now, the car is rough on starting up (idles rough) and stumbles when you initially give it gas (push on the gas, and the engine slows), but once it starts going, it drives as smoothly as before.

Anyone know what the plug was for, and should it be left unplugged or plugged?

Thanks!

[christophbmw]

pictures?

[bm318ist]

if this plug is taped up to the computer harness, leave it unplugged!
this wire is for non cat design(catalytic converter).