The symptoms you suggest sound a lot like LSPI (low speed pre ignition). The engine is not supposed to do it, but its a sympton a number of new small capacity highly compressed engines have experienced (I work in this industry) . There are various reasons why this happens, some is down to lubricant, some is fuel quality and some is engine Configuration. I'd go with what has already been suggested and get the software checked this could well resolve the issue, if it's happening. If someone is able to take a cylinder out, it will have small pitting. Hopefully it's not this, and just some sensor issues, but all oems have suffered the effect and it would be surprising if any garage had ever heard of it in order to diagnose it..
The symptoms you suggest sound a lot like LSPI (low speed pre ignition).
If it is that and is just a feature of the engine do you think it will get worse? The garage confirmed it has the latest software so all I'm trying now is better quality fuel.
If it is (big if) unfortunately yes it will get worse when you'll get 1 or 2 instances of mega knock and the piston will shatter. Like I said it's a big if, but on your side it is well known and you would be unlikely to be out of pocket. Unfortunately as I said, it's very hard to diagnose unless it goes and has some rather expensive kit hooked up to it. The Ford ecoboost has the same problem, some engine configurations can remove the instance, but the engines are normally designed with parts and timing maps to counter it as mu h as possible.
However that said, you said you've tried different fuel types, have you run Shell Nitro and experienced the same thing, the burning characteristics of different fuels can sometimes mitigate against it, it's more interesting to know as it would not be a viable "fix".
If you've got a bit of a geeky mind google Infineum LSPI effects, it's a good eye-opener to the phenomenon.
Let's hope for sensor issues though!
Sui..
So we are now back with engines that pink?
Funny, I was just thinking that.
Pre-ignition is something that should quite quickly be picked up by the knock sensor and corrected though, and it probably is. The big question is why it would be a problem at a specific engine speed.
My guess is it'll be something like the fuel injection drops an injection stage, but the switchover isn't handled smoothly.
Duncan, yes unfortunately so. The drive to downsizing and highly boosted engines is throwing up all manner of issues. Knock sensors will only operate within a specific range, and LSPI is not something they can dwal with too well. The problem is more persistent at cold Temps under load, think car shuttling at ports.. Part of the problems come from ring packs letting too much lube through as part of the design, leading to heavy hydrocarbons being part of the fuel mix or Injector deigns causing wall wetting within the cylinder with the heavier aromatic ends in the fuel igniting at different points.. Its a very complex issue that designers are still trying to get to grips with.
To be fair high boost lean burn it's almost inevitable.
I'm a long time out of the car trade and I'm glad!
So a combination of design of low resistance/wall pressure rings and extremely thin oils 0-20w typically , is causing the inevitable problems, oil usage with some modern engines is a big problem leading to oil starvation impacting the cam chains too ..
Any ideas what I could do to fix it? I noticed today driving home from work that the 'hiccups' occurred even if I was very light on the throttle. Only in 3rd gear. Flooring it in second was fine.
So confusing!
Or if anyone has recommendations for a replacement for a Skoda Yeti? I'm very tempted to sell and move onto something more reliable. Really miss my old Fiat 500. That was a great car.