Hi folks!
My first post here. I have a weird issue with my -07 Mazda 6 diesel, and maybe someone here has had this problem before.

The problem is rough running between approx. 1500-2300 rpm when the engine is warm. When I start the engine cold, it takes 1-4 minutes after temp indicator has reached normal temp then the engine starts stuttering. If I press the accelerator the stuttering stops and the engine runs normal again (while accelerating).
It runs smoothly on idle, and on all rpms if standing still with no gear in position.
It only runs rough on low to intermediate power and constant speed. (So a workaround is to constantly change speed, but that's no long-term solution...;-) )

Driving on the highway today I noticed the fuel consumption increased to 0.8-0.9 l/10km for approx 10 minutes, and then the engine was running smoothly. Then it went down to "normal" 0.5-0.6 and the roughness was back. I suspect it could be the cleaning process of the DPF causing increased fuel consumption?

The car was serviced by Mazda recently.
The DPF light is not on.
I have had the car checked for any present or stored fault-codes, but there are none.
I have cleaned the MAF, no change.

Thoughts anyone? A clogged DPF? Why isn't the problem there with a cold engine? What changes when the engine reaches normal temp?

Best regards,
Markus

 

I'm having the exact same problem, exact same car

At least reading this I know there's probably little to gain by getting a service.

 

I sugest replacing SCV valve on the fuel high pressure pump.
A friend of mine having the same car had this problem and i replaced it for him and everything was ok after that
Kinda easy to replace. I leave a youtube video link here
Hope it will help

 

Agreed : SCV is a likely candidate : In case it helps anyone else, here's the story with my 2010 Mazda 6 2.2 CD diesel 120k miles.
I had a similar problem for months. In my case revs unstable and power sluggish / stuttering a bit between about 1300 - 2000 rpm. Especially around 1500 rpm. With higher revs >2000 rpm it was running smooth and power as normal. Quite a sudden change in performance at 2000rpm or 2100rpm some days.
The work-around before i figured it out was to always always change down a gear if there was any chance dropping below 2000 rpm e.g. corners / traffic / hills. The problem was some days worse than others... couldn't be sure this was air temp / fuel brand related or what . Didn't appear to be consistently better or worse with cold versus warm engine.
Garage changed the fuel filter which gave some marginal improvement for a few weeks. In the end the engine started stalling as I slowed towards lights etc. But for ages (24 months) it never was bad enough to stall and I couldn't diagnose. Looked up the new symptom (stalling) and pretty quickly found the SCV is a candidate cause. Changed the SCV for a new Denso one and hey presto : fixed.

 

And BTW replace SCV is a pretty easy job. Battery out then unclamp and bend up one rubber pipe/duct for access and then two screws. See you tube - 20 mins tops.