No acceleration and Helicopter noise on motorway on startup

[CarZ0]

My Jazz is difficult to accelerate past 50mph and make a helicopter noise when I go straight to driving on the motorway.

The sound and acceleration problem goes away after about 5/10 minutes and I haven't experienced the problem twice in one day.

Thanks for the help!

[Marco1979]

Hmmm, I would have a look at all 8 spark plugs first. Maybe when cold one or two of them do not fire properly. That would explain less power and noise because of fuel burning in the exhaust system.