High idle, noise while turning

[conjuay]

Hi, I'm new around here, so forgive me if these questions have been addressed previously.

'85 325E: idles around 1200 -1300 RPM, all the time. Can't find any info in owner's manual or Haynes book as to what the idle rpm should be, or possible causes.
Any ideas?

Next question: On tighter turns, I'm getting a rumble/grind from the rear. I'm hoping it is just low oil level in the differential, but considering the cars age...

Finally, where can I get the service code reset tool relatively cheaply?

[witeshark]

About the noise from the back, that's almost certainly a need of new gear oil in the differential.

[conjuay]

Originally Posted by witeshark

About the noise from the back, that's almost certainly a need of new gear oil in the differential.

That's kind of what I was hoping... I'd hate to have to try and find a 25 year old differential!
I did notice on the emissions tag under the hood that "ignition timing and idle speed: No Adjustment Required"

[conjuay]

Well, the diff oil wasn't it. There was some foam in the old oil, and the noise seemed to stop for a day. Then last night a right turn in a parking lot brought it all back, a deep rumbling noise from the rear of the vehicle.
Any ideas on how to proceed? There are some rubber couplings that look almost like the old front axle 'donuts' that were on the Saab 96's from the sixties, but I don't see any physical damage on those... Then, near the wheels, there are CV joints, but CV's usually chatter when they go bad, not a groaning sound... and CV's usually show boot damage,which I don't see.
I'm hoping some of you seasoned people will jump in with ideas on how to proceed...
TIA
Mike