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?