Patrol 4500 Ti Cold idling problem

1998 model. I have a problem with a "dead spot" on the accelerator at low revs when the engine is cold. When you start to put your foot down to accelerate from a standing position there is a complete dead spot and it accelerates and stops sporadically. If the accelerator is pushed past a certain distance of pedal travel it accelarates normally but not in the first part of the travel. After reaching normal operating temperature it seems OK but not perfect. I've been told it might need the "idling unit" to be replaced - approx $500.00 worth - but was wondering if anyone else knows whether this is true or has experienced this problem?