Oxygen sensor???
 

New to Porsche and of course the forums. Just got a 87 924s. A couple of ??'s. Next to the oxygen sensor there is another nipple. what is that for? When deaccelerateing there is a clank in the rear. what would that be?? Thanks in advance.

nipple is for a second sensor. japan version.

OR...
The second nipple is for the exhaust test pipe that goes up to the rear of the cam.

Most of the test pipes have rusted out and are discarded. Put a solid cap on the nipple or use the compression fitting and a ??? screw head to seal.

Clank in the rear is usually...
1. CV joints need repacking
2. Change the trans axle fluid to RedLine MT 90. Catch the fluid to see if you have flecks of steel = bad.
3. Rear axle bearings
4. Worn shocks
5. +++++

Gl
J_AZ

From an older post:

If you get the sound when you're sitting still while revving, it wouldn't be the CV joints. However, if you're only getting it when actually driving, that sounds like the joints to me. For some odd reason the CV joints on these cars cause grease to disappear to nowhere and thus require periodic repacking. Just remove it and repack. If you're feeling more mechanically inclined, you can take the joint apart to inspect for wear as well while you're in there.

IF the sound happens while at idle, it could be your torque tube. The bearings on them can get misaligned when they get old and thus can get more and more noisy. Eventually, you'll just have to replace the tube.

ausgeflippt951

The test pipe nipple can be covered with a Lug Nut.