I'd start there. If you can find a used ICV that you know is good, swap it in and see if that fixes the problem. Also - you can try and clean your existing ICV and see if that helps. Sometimes they get clogged with gunk and can't operate as they should.

if your car doesn't have an ICV valve, then I'm afraid I'm out of ideas.

Good luck.

Troy
1995 E420 75k