Code 51 will occur if:
the throttle is pressed while in diagnostic mode or there is a problem with the IDL switch in the TPS
the A/C is on while in diagnostic mode
an automatic vehicle is not in Park or Neutral or the Neutral Start Switch is defective
All of these will cause idle problems and timing can not be set with any of these problems present.
EDIT: check the throttle cable for excessive play... AFTER you fix the other problems. The TSRM covers adjusting it.
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