560sl accelerator sticking

I looked at an '87 560sl today and it had a problem that worried me. Whenever I floored it, the accelerator didn't return fully back to the idle position. It would only come back until the engine was turning about 2k. I had to reach down and pull it back. If you slowly pressed it to the floor it would return normally. Has anyone run into this problem? I'm not at all familiar with what linkages a MB might have so I got concered that it may be a more expensive fix than I would think it would be. Any ideas?

Brett