The car is designed to do what it is doing, the ecu is seeing the revs rising whilst the tps is at 0 and goes into decel to control the revs once the revs are low enough go back to normal and the revs climb again. It will keep repeating the process! My rb26 was doing this for ages and no mechanic could fix it! I end up finding the problem myself, mine was a bent butterfly on cylinder 1, ur engine is getting a significant leak from somewhere between the throttle and the head. Could be buggered throttle shaft seals or any of the gaskets between there snd the head! Even the injector seals! Either way its a air leak.
How much boost were u running when it happened? What engine and where are u? I could give u a hand to try fix it if u r local to me