380 SE ABS light / Idle strangeness

I have a 1985 380 SE with 100,000 miles. New idle speed control box, timing chain and exhaust in last 4 months. Car runs very well, but starting last night, will NOT idle, but can be coaxed beyond 1500 rpm, where it runs well. At all times, yellow "Antilock" light on dash stays on. I have swapped out the OVP relay out of a working 380 SL, no change.

Any ideas?

Thanks to all.

Cheers,

John