E34 Electronic Throttle Control Troubleshooting

I have 1995 525iT with ASC + T that is acting up. The throttle is 'sticking' open causing dangerous situations. The problem is not predictable. I cleaned and lubricated the mechanical throttle linkage parts and this has not solved the problem. I also cleaned all of the electrical connections at the throttle assembly. Still no joy. Checked Bentley manual and there is no description of how this system works or how to troubleshoot. Can anyone help me with description of how electronic throttle control works on this car or troubleshooting tips? I don't think it is exactly like the EML throttles on earlier E34s. I am pretty sure control is handled by ASC + T system as opposed to separate EML computer.

Mark
89 535i 5 spd
95 525iT
88 Celica GT4
92 Celica GT4 :(