Yaris not running smooth

[JDMCD]

Hi all I’m new I would like advice or help. I have a 2015 Yaris 1.3 petrol I’ve had it about 6months it only has 21,000 miles on the clock it has been going beautifully until about 2 months ago and now it’s running a bit uneven between 50 to 60 mph I’ve just had it serviced new plugs and everything else and it’s made no difference I would be grateful for any help as to what it could be. Thanks 

[flash22]

Auto or manual ? If manual what gear are you in at that speed ?

[JDMCD]

Sorry I should have said It’s a 6speed manual gearbox and I’m in 6th gear when I hit 40mph

[Perfection]

Is that the right gear (sixth gear) at 40mph? 

[JDMCD]

It feels right and it’s smooth until I reach 50 -60 mph and then it runs unevenly it will keep accelerating up though it and will hit 70mph no problem but I like to sit around 50-55ish 

[flash22]

Changing up too early, any codes or eml ? was your last car a diesel or larger cc ?

[MagicBoy]

Wheel balancing? Can cause vibration at those speeds if a balance weight has dropped off.

[Madasafish]

Do you do short journeys most of the time?

 

It may just need running at higher revs to  clean out the crud caused by stop/starts at low speed when cold...

[bathtub tom]

I've noticed a harsh spot in my 1.3 petrol Icon at around 1800RPM if I ask the engine to pull too hard. That would be about the same as the OP. I tend to change up in the higher gears now when I know the revs will be above 2000.

As a rule I now use 4th at 30MPH, 5th at 40 and only change up to 6th above 40.