Rough idle once hot - VIDA help

[Decky62]

Hi, ive got another post somewhere regarding this. Finally managed to find a cheap cable that works with VIDA. I could do with some help deciphering all of this. I have a rough idle once the cars hot, it will level out if I have the AC and fan on but it is getting worse.

https://www.volvoforums.org.uk/showthread.php?t=328518

[ca2n]

Any DTCs logged?

[Simmy]

scan the car read all fault codes. then erase all fault codes .run the car and repeat to find any current faults. read the modules which have codes .then diagnose what is causeing the codes read live data to delve deeper .use the advanced tab. watch some vida tutorials on youtube to help you navigate through vida use.

[Decky62]

Hi, thanks for that. I cleared the DTCs and took the car for a spin, the idling seems to coincide with the ECM and CEM errors. Images attached.

[ca2n]

I've had a look at the CEM-U030100 and ECM-U032200 DTCs on VIDA and they suggest some form of communication error between the CEM and ECM or faulty software in the ECM. You can have a look at them for yourself under Information --> Fault Tracing --> Diagnostic Trouble Codes and Associated Procedures on VIDA.

I'm afraid there's not much more I can advise apart from going to Volvo or a specialist to see what's up with the ECM software. I don't think it's worth going further with replacing parts, troubleshooting, etc at this point until these two related DTCs are resolved, but happy to be proven wrong.

Best of luck.

[Simmy]

i see you are using vdash as well as vida . try unplugging and cleaning the contacts on the cem plugs dont forget to disconnect the battery before unplugging any thing. has the car had a remap? it could just be a low quality remap.and be over fueling.

[Decky62]

Is the cem behind the glove box somewhere? The car has had a BSR remap in the past but it’s currently back to original. I have spoke to BSR and they say it has nothing to do with the remap. They say it wouldn’t affect the idle. It’s annoying because the car works fine, but the rough idle annoys me and I want to get to the bottom of it. Any ideas on the PTC heater message? I have got an interior temperature sensor to fit that seemed to remedy if for someone.

[Decky62]

The idle is far better with the AC on when the cars hot. The higher you speed the fan up with the AC on the better the car runs!

[Moose Test]

I'll wager you one beer token that this absolutely is down to the remap.

The "software incompatibility" errors likely refer to changes to CRC / checksum data made to the software image(s) when the map was installed and/or removed. That, or FW version differences between the affected modules that aren't acceptable to the CEM, again, because they've been changed from the factory standard by a non-Volvo system and aren't being recognised as being interoperable according to the software in one or other of those modules. i.e. the CEM is seeing this as software "corruption".

Again, a theory but - your currently operating map isn't correct for a low engine load portion of the fueling / timing curve, at normal operating temperature. Turning the AC on and adding additional electrical loads loads the engine and brings it back to a point on that curve for which the map data is correct.

[Simmy]

what did the car run like when the bsr remap was installed if it was good why dont you re install the map... have larger flow injectors been fitted to run alongside the bsr map? try calling shem at shemtec automotive he may have some advice he can give you.