Is it locking up as in seizing, or do you mean shutting down and not responding to throttle input?
If the engine is just shutting down to idle, it could be a speed sensor. Back in ‘96 my ‘90 started shutting down to idle while cruising along at highway speeds, down shifting nor flooring it had any effect, then after a few seconds the engine would just come back to life and perform w/o issue. It took about 16 months and 3 trips to the dealer before ecu ever registered a code. It was diagnosed as bad speedometer speed sensor, the sensor was telling the ecu that vehicle wasn’t moving, causing the ecu to shut everything down.
