1984 928 S2 Auto Euro
Was just mucking around under the hood and found this round 3 prong plug lurking just next to the air intake in the pic.
Wondering what it is for, is it maybe for connecting to the computer, although I don't think so.

 

It's just some sort of test port used by the manufactor/dealership if I remember correctly, not used anymore, obsolete, just put the cap back on and forget you ever saw it.

Brian.

 

Thanks for that I will make up some sort of cover and forget about it

 

Normally, if that cap is missing or has been dropped...it's right below the air cleaner housing, beneath the u-shaped rubber fuel hose, right next to the spark plug boot.

Don't ask me how I know this...

Brian.

 

It's a little bit of a guess on my part but I would suspect it is the "TDC Mark Sensor" as shown on the RH side of the wiring diagram for the Front End and Engine, Electronic Ignition/LH Injection. Denoted as (Only For Adjustments).

 

Yep - It triggered an NLA timing light at the dealership...