740 Turbo Revs between 2K-1K

[Katrina]

Help! My 1989 740 Turbo sedan began revving this week. Say I'm at 2K
RPM, then I let off the gas. As soon as it hits 1K RPM, it revs back up
to 2K, then back down, then back up.
Any ideas?

 

[James Sweet]

Help! My 1989 740 Turbo sedan began revving this week. Say I'm at 2K
RPM, then I let off the gas. As soon as it hits 1K RPM, it revs back up
to 2K, then back down, then back up.
Any ideas?

The usual cause is a vacuum hose has come off under the hood somewhere.