Do you have any diagnostic codes stored? If so, what?
You should go through the troubleshooting chart for ignition problems in the from of the section I linked to. The diagnostic work flow Toyota specifies does work really well. As this is an intermittent issue it probably will be abit harder to diagnose... try to recreate the conditions under which the faults occur: If they usually happen after the car had been run for a while try warming the parts with a hair dryer or hot air gun (set on LOW). If the problems occur when cold, make sure the parts being tested have had time to cool sufficiently.
Troubleshooting work flow:
http://www.cygnusx1.net/Supra/Librar....aspx?S=IG&P=3
Sure, the igniter is a possibility, so is the CPS and ECU. Start with the work flow.