Clunk when shifting into reverse

[JamusMcFamus]

'79 528iA, 106,000 miles

When I shift from park into reverse, I usually get an audible "clunk" coming from the transmission. I've checked that the fluid is at the correct level, so that's not it.

The car shifts well in Drive, and doesn't display any weird behavior. I have noticed that if I put it into drive before I go into reverse, the clunk usually doesn't happen.

Notably, the car has a high idle (~1500rpm) upon initial start-up.

[T.Hanson]

High idle on start up begins with the Aux air valve. Older nemo style or newer version on the valve cover. You can read the FAQ on how to check, clean and adjust either type. They get cruddy and stick, don't do what they are supposed to regulating airflow vs. mixture on cold start up. Usually less noticeable in summer.

Other high idle possibilities require proper timing, then the adjustments on the Air Fuel Meter (AFM), throttle body, throttle switches.

Reverse clunk is probably worn drive shaft components. Inspect guibo, universal joints, center bearing for any extra sloppy. High idle is spinning the tranny, to transmit the torque harder, to whack the not new connections.

[JamusMcFamus]

Thanks!

[GripGreg]

Tom is, of course, correct! But I know he meant FAQ, not FAC. It's a bitch to be human, huh?
In my case, it was the guibo, the donut between the driveshaft & the tranny.
If that is your situation, make sure, that, if your guibo has arrows, the arrows have to point to the bolt heads!
If not you'll have the same issue next year.
If your style guibo doesn't have arrows, no problem.
And, I found out to replace with the very same style guibo, for some reason.
Maybe someone here can explain why that is?
Good luck,,,,Greg

[JamusMcFamus]

Perfect, that's the first thing I'll check, then.

[GripGreg]

There's a major reason for the high idle.
Again, Tom is correct; check your auxiliary air valve.