Again, you mentioning this, it triggers possible overboosting , hence possible limp mode again. Larger exhaust obviously promotes more flow through the snail, hence more boost, which possibly triggers limp mode.
One of limp modes primary triggers is overboost. ZD30 crd are very sensitive to this...
However... You mentioned it played up idling this morning ??? When you say idling, you mean putting along slowly out of driveway?