G'day,

I have a VS Series 1, 3.8Lt V6, 5 spd manual, on dual full that has a flat spot issue.

When the engine is cold there is not flat spot at all, but as the engine gets up to running temperature, the flat spot issue shows up and it only occurs once I hit about 2000RMP.
It keeps accelerating past 2000, but with far less power and it surges.

This problem occurs regardless of whether I'm running on gas or petrol, so I'm guessing it is a sensor/ignition issue. But I'm not really sure where to start.

I have replaced the spark plugs and spark plug leads, this helped a little, but the problem is still there.

Any suggestion would be appreciated.

Thanks.