zafira engine hiccup

Hi folks, new to the forum. Hello to all.
Hope someone can help me out.

I have a Vauxhall zafira design 2009 1.9cdti 120
It has a single hiccup only under a specific condition.
When I accelerate the engine gives off only what I can describe as a hiccup, it feels like it misses a single beat and then is fine.
It only does it between 1600-1800 rpm.
It only does it when accelerating but if I accelerate as slow as possible it doesn't
It only does it when the air temp outside reaches 17 celcius or warmer and the warmer the air temp the harder-bigger the hiccup
It doesn't do it when towing the caravan
There are no codes
I've had it at a vauxhaull garage and they have no idea
I've had it at my general local garage and had the following work done
New dpf
New dpf sensor
New dpf sensor supply pipe
New egr
New battery
Inlet manifold cleaned
Throttle actuater cleaned
New air flow sensor

It's so frustrating
Has anyone got any sugestions please
Thanks