Toyota Repair: engine surges, throttle position sensor, head gaskets

Question
1990 3.0L 4x4 p/u 426,000kms engine surges between 500 & 1500rpms when brakelight switch is activated but only when engine reaches operating temp

Answer
Is this an Auto Trans? Is the Air Conditioner on during this malfunction? Possibly a bad EGR modulator or the TPS sensor (throttle position sensor). The 3.0 Toyota V-6 was involved in a very large Toyota service campaign to replace head gaskets due to poor design. There are several minor circumstances that may cause what you describe due to the expansion of components at operating temp.