go to your local junk yard.. they usually they have no idea what it is & u tell them that it's a "coolant thingy" & they charge me like 5 or 10 bucks! worth changing for that amount.

but as far as the car bucking like that.. normally if they IACV is having issues the car will just idle up & down real funny while u'r sittin there.. bucking it not a normal symptom.. u might want to look at your ignition or fuel system for the bucking related issue.