Rough idle when hot
 

My S80 has developed rough idle when engine is hot and only when hot. Engine is very quiet and steady when cold and has absolutely no indication that anything is wrong. Car also pulls with no problem (hot or cold), power is there when you need it and floor it. Fuel consumption is normal and also there's no smoke whatsoever. There is some smoke smell in the cabin though, but only when engine is hot. I don't know if this is somehow connected to other two issues I have:

- RPMs start to fluctuate when coming to a stop (breaking or cruising - a bit more evident when breaking). Engine won't stall, but it definitely drops significantly. But as soon as I stop this big fluctuation stops, but then that rough idle comes in. This is not happening if I step on a clutch (coming to a stop breaking). As soon as I release the clutch, RPMs start to fluctuate (coming to a stop breaking). This problem is regardless of the engine temperature.

- When car sits for a while (let's say 8hrs) it starts "weirdly". It turns over but it will hang on 700 RPM for a few seconds and after that it will jump to > 1000 RPMs. Meanwhile nothing electrical is working (no lights, gas pedal not responsive, no radio, no fuel capacity level, ...). I can also hear that in this short time the RPMs are slowly rising and after that RPM jumps again to a 1000 RPMs. So it's something like: first stage fast rising to 700 then second stage slowly rising to 700-710ish and the last stage fast rise to 1000. This is only happening sometimes, but a lot more often lately. Please see the video below.

These two problems were already present when I got the car on 01.10.2019 @298.000km.

Rough idle dissapears when I turn on the AC, as the engine gets more load. Other two problems are not affected by the AC.

Service history (chronologically):
- Oil and oil filter changes are made on 10.000-13.000km interval w/ Castrol Edge 0w30 A5 and OEM or MANN filter
- Fuel filter 10.10.2019 (FRAM) 298.000km
- MAP sensor (Bosch) 11.12.2020 @333.000km
- Cleaned Throttle body 11.12.2020 @333.000km (also changed the gasket)
- Fuel filter 23.03.2021 (OEM) 340.000km
- Air filter 23.03.2021 (OEM) @340.000km
- Rough idle started 17.08.2021 @353.000km
- EGR clean (not thoroughly, only what I could manage to scrape out) 05.12.2021 @360.000
- Fuel filter 25.02.2022 (MANN) @367.000km

VIDA shows no trouble codes.
I'll be more than happy to fetch you more data if you'll need it.

Attached:
- First two videos show that "weird" start, the third video shows that RPM fluctuations when breaking and rough idle (at the end of the video). This one is a bit shaky - I'm sorry for that, I can also try to record a better video. Also please turn up the volume at the end of the video (on this third one) to hear that rough idle. The last video is just idle engine (cold).
- Images from Vida showing different parameters. This was recorded when engine is hot. Interesting is that one image showing injectors (one having a 39 r/min difference is quite big, right?).
- Image of inside of EGR valve after cleaning

Car:
Volvo s80 2.4D D5244T5 M66 my2009

Weird start #1:

+ YouTube Video

Weird start #2:

+ YouTube Video

RPM fluctuations and rough idle:

+ YouTube Video

Engine idle (cold - so the IDLE is fine. ther's some popping noise tho):

+ YouTube Video

Really dont know what could be. Also VIDA dont show error on my D5, but when it's warm engine and if I press clutch while slowing down, rpm are jumping like by you. Once I drove 80.90 kmh and pressed clutch, put in neutral and let clucht and after 5-6s jumping rpm, engine stalled. Also waiting on traffic light rpms are jumping.

The worst is on my engine if it's in neutral and clucht is not pressed, then rpms are getting crazy

That noise wjen remove fuel cap can be ftom vaccum pump. Soon I will change engine mount and while there, I will see what is with valve on vacuum pump. If I find problem, I will let you know.
I dont hear strange noise at all. Mostly is from injectors

Currently I'm not at home, so I'll record a video of rough idle later and post it here. This video of cold engine idle doesn't show that I know, I'm sorry. Although one can probably hear some bad hydraulic lifters, but that's off-topic.

We need to change them asap. Around 300€ parts with sealings and 250€ is work in my country. Probably I will go in summer there and change them

So I tried to record that rough idle and it just wouldn't... So if it's so "random" at same conditions (same fuel, same whether and same driving conditions) we can guess that something is dirty, seized up or clogged? If it's faulty sensor then I guess that roughness in idle would show every time the engine is hot?

I want to post an update as it has been 3 days without rough idle. Possible solution was 1 liter of "Antigrippante 25" diesel additive into the 1/4 of a tank and then blast it on the highway. I'll pour another liter of it when reserve will come up and come back with the results after 2 weeks I guess.

That weird cold start up is still unresolved if someone has any idea, I'll be grateful.

You are from Slovenia?
If so, go to that Volvo guru in Maribor. He use to work for Volvo and now he is Volvo independent mech. I made termin by him last year but corona...

Yesterday I put another liter of Antigrippante 25 in the tank on a reserve and blast it on the highway. Currently the engine runs really smooth without any roughness in idle, so I guess that's it. I'll still clean the EGR valve when I'll have time.

Yes, I'm from Slovenia. You mean Bauman? I guess I'll have to stop by to get this cold start up checked. For now I'm guessing the starter motor maybe. It has some weird sound to it.

Yes, his is the guy. If I would drive 700km to him, you can also 70 km :)

Guys from Volvo SLO are calling him when they cannot resolve some case

I will ask friend to send me that from SLO. And say Janša to resign me in books of born in SLO. They deleted me in war lol