1987 325ic - ABS activating while car is at a stop

Intermittently, the ABS on my 1987 325ic activates while I am at a full stop with my foot on the brake. An example is when I am waiting at a traffic light. When I lift my foot off the brake the ABS stops pulsing but recommences when I press my foot back down. It appears to happen when ambient temperature is high (80s+). The last time it happened the "Anti-Lock" warning light lit on the instrument cluster. The fluid is fresh: pads and rotors are good.

Uncharacteristically, Bentley just says that troubleshooting the ABS system is beyond the scope of the manual. I will visually inspect the sensors and pulse wheels when I get time (July), but I am hoping this symptom is diagnostic of something really specific.

Any ideas what is causing this?

Kind of sounds like a sensor it going crazy. Those are hard to diagnose, especially since it happens at a stop. I use to have an Acura that the ABS would do weird things at speed, turned out that one of the pulse rings had rusted and snapped, causing a larger gap and fooling the ABS into a locked wheel.

So I think you are on the right track to inspect all the sensors and parts. Be sure to clean the pulse wheel and sensors, it could be it is just not getting a good reading b/c of dirt build up. Not keeping my fingers crossed on that one though.

Does it at a dead stop or as you are coming to a stop?

So far, only at a dead stop.

Sounds like it could only be caused by the computer or a wonky ABS relay. I'd replace both. If you can't find any locally, let me know, I have spares for cheap.

Update:
Finally found a day to spend with the cars (funny how a imminent track day does that) (Friday - Thunderhill). Inspected all ABS sensors; both rear sensors were horribly clogged with crud. Fronts were fine. Cleaned all and replaced.

Moosehead: Not sure what relays you're recommending. Are they #13 & #14 on the attached or #2 & #3?

I bought #13 in the attached. Did not buy #14: Double 02 Salvage wanted $140 so a bit much to pay speculatively.

This is one of these problems that may not rear its head for months again, so not sure if I fixed the problem just cleaning the rears. Time will tell.

Looks like 14 is the ABS ECU; 2, 3 & 13 are the relays.

UPDATE:
Duh. Checked the sensors (thank you, granthr). Both rear sensors were massive blobs of crud; one of them looked like there was a metal sliver stuck in the muck. Fronts were pristine. Cleaned everything; so far so good, but it's only been a few days.

Brian glad to help! Sometimes the simplest things can cause the biggest problems and we just assume a complicated solution. I hope that is all it was and it continues to work for you!