Try cleaning out the idle speed controller it probably is full of carbon and is not working. If you take it off the car there should be some screws that you can use to take it apart and clean things out.
check your timing. make sure you jump the terminals. heres where everyone gets info on anything and everything about doing work on the A70 supra. http://www.cygnusx1.net/Supra/Library/TSRM/MK3/default.aspx
Coolant sensor or Mass Air Flow needs replacing... Have had to replace both on my two A4 2.8. Computer diagnostics can tell you which one. Buy on line dyi and save hundreds from what dealer charges!!
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