We have been trying to solve this for almost a month now.
Head gasket went, due to the driver continuing to drive the car (topping up with water, etc). The head has been replaced with a reco unit (inc cam, valves, etc). The following has been replaced as there was goo through everthing:
Idle Control Motor
AFM - Was reconditioned (and has been sent back twice to confirm it is set correct)
The fuel injectors were also serviced.
When the engine is cold, the car runs fine, and the mitures can be adjusted correctly. When the engine reaches operating temp, the car starts to hunt, and is slow to respond to throttle movement.
We have put a scanner on the car, and everthing we can see is fine.
Cold - 110 115 110 115 110 115
Hot - 120 120 120 120 120 120
The only thing that is strange is the vacuum, which is 8 mercury.
We have checked injector pulse time, and the reference signal, both are fine.