What is this?

[fudge_sta]

Hi,

Whilst giving the my car a quick service i came across this connector/sensor that had broken somehow and wasn't connected to anything from one end.
It is located just under the obd1 port in the engine bay. (see pic)
My question is what is it and is it important? Car is facelift 325i cab, manual.

[Grrrmachine]

Under the OBD port there are two connectors: the CPS and the CID

If the CPS was disconnected the engine wouldn't start, so it's most likely the CID:

http://www.e30zone.net/e30zonewiki/index.php/CID

Check your HT leads to confirm.

[fudge_sta]

HT leads are all connected both at dizzy cap end and on the block although the connection for the CID is not there. I'm thinking it must of previously been there.
Is it a simple case of buying the new CID wire and connecting it as pictured in the wiki? or will the car run without this?

[Billwill]

It will run but I believe fuel economy may suffer somewhat.

[fudge_sta]

LOL This explains a lot!

[Brianmoooore]

Car will run happily without the CID sensor, but will run that little bit better with it.
The cylinders in your car are arranged in pairs, with one of each pair being at the end of its exhaust stroke when the other is at the top of its compression stroke. Without the CID sensor, the ECU can't tell which is which, and doesn't know which one to inject fuel into, so it injects fuel into both.
The thing that would worry me the most is what kind of muppet owned the car before you to leave the car in this condition, and what else he has supplely messed up.

[fudge_sta]

Hopefully nothing else left hanging or messed, have gone through the rest of the engine bay whilst servicing and all seems ok for now although i am no expert.