97 probe gt - engine throb a cold idle HELP

1997 GTS just started severe engine throb after a cold start. In idle, RPMs settle in about 1,800, race up to 3k, settle back, race up again, etc. Is this something to do with the fuel injector chips, the coldness of the air (it has been below 20F here), or something else? Anyone else with this trouble?

Car runs great once warmed up or after it is put in gear...