Given older ASR is a electric motor / clutch that pushes the throttle shut, I'd be tempted to remove these parts and connect the throttle blade directly to the accelerator linkage. Also make sure the throttle position sensor is working.

Or, there was a dyno mode that disables ASR. One of the tuners in the day offered a super expensive kit to shut ASR completely off, turns out they were triggering dyno mode each time the car was started / bypass sw pressed. There might be a thread on this site outlining how it was done. .