I am having the following problem with my F18B2: while the engine is warming up it has a slight hesitation to rev up from idle: as soon as a touch the gas pedal it nearly stalls at first but then starts to rev up normlly after a second or so.
Just after the engine is cold started (high idle) or with the engine already warmed up there is no problem. It just occurs while the engine is warming up.
Automatic gearbox in neutral or in drive makes no difference.

Following has been done:
IACV and throttle body cleaned
Valve clearance adjusted
New spark plugs/air filter
PCV valve replaced
New coolant fluid (done by dealer)
ECU reset

The idle speed is ok: checked both with and without load.

Thanks for your help.

 

engine wires? fuel pump?