Engine Jerking After Auto-to-Manual R154 Swap - ECU Reset Fix

Transmissionbeginner✓ OP Confirmed

Problem

After swapping a 1987 Supra NA from automatic transmission to an R154 manual from a 1988, the engine began jerking badly at higher RPMs. The owner had initially jumped the neutral safety switch and unplugged the automatic transmission control module from the passenger kick panel. The car ran smoothly for about 30 minutes, then the speedometer stopped working and the engine jerking began simultaneously.

Engine jerking/bucking between 2000-4000 RPMJerking more pronounced under engine load but also noticeable in neutralSpeedometer stopped working at the same time jerking beganSmooth idle but rough mid-range RPMsWeak spark observed

Root Cause

Disconnecting the automatic transmission control module from the passenger kick panel caused the ECU to enter a fault state or limp mode, resulting in engine jerking. The ECU needed to be reset to clear stored fault codes from the transmission module being unplugged.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted November 2024 on SupraForums.com