One problem related to ignition module has been reported for the 1999 Toyota 4Runner. The most recently reported issues are listed below.
The following work order was given to me. Found dct # po420 ineffecient catalytic converter. Tested a/f sensor it was good, it measured 1. 8 ohms. Tested 02 sensor it measured 19. 0 ohms n@ 1800 degrees. Diagnosed switched grounds at e. C. U. E10 # 8 and # 17 . Removed and switched wires to the correct positions. Eraced code in ecu memory.