Hesitant running

I have a 2013 Mazda CX-5 2.2 150PS diesel manual with 72,000 miles and a full service history. It has a frustrating intermittent issue which is most prominent when the engine is cold and is being driven at low speeds and revs, such as in heavy traffic, where the engine hesitates slightly, almost like a flat spot. On the open road and with your foot down, the car has plenty of power. There are no warning lights or DTCS stored. I’ve fitted a new fuel filter and cleaned the MAF, and the car has been running with fuel cleaner/ additive for some weeks. Ian

First, have a look at the engine management coolant temperature sensor (CTS) and check the recorded engine temperature while warming up to see if the results are plausible. The easiest way to do this is with an OBD reader linked to a PC or smartphone. Also, wiggle the wiring to the CTS (which may be a separate sensor from the one used for the dash display) while watching the temperature, to ensure there isn’t a wiring fault.