Engine speeds B5244S2 flucuates at warm engine idle.

mod64 · Post by **mod64** » 10 Oct 2021, 09:51

Hi,
since a short time I noticed my V70 2001 B5244S2 petrol engine starts idle speed fluctuating between indicated 800rpm and 1000rm in fixed intervals of 2 or 3 seconds only when the engine is warm. The ETM has been replaced 80000km ago, so far no problem at all.

In general the engine starts/stops great, power/torque is pleasant. Sparkplugs and Ignitions coils recently replaced with no effect on the idle speed fluctuation.
Start moving the vehicle without pressing the throttle pedal but only releasing the clutchpedal slowly works smooth.
With VIDA I could also see the problem is not the ETM (actual and target values are similar) nor the igintion as such gives any indication.
The voltage level of the rear oxigen sensor appear low at idle speed ( 1,06V) while I expected 2V, could that be an indication?
I noticed there is no difference between AC on / off.
No faultcodes are stored.

Any clue what to check further?

Cheers
Rob

Post by **vtl** » 11 Oct 2021, 09:08

Check short term and long term fuel trims.

mod64 · Post by **mod64** » 11 Oct 2021, 09:37

You mean the adaptive setting for fuel injection?

Post by **vtl** » 11 Oct 2021, 09:43

Yes. Engine computer has to compensate for vacuum or fuel leaks, it tells you almost certainly if you have any intake holes.

mod64 · Post by **mod64** » 11 Oct 2021, 09:47

Thanks, will check it with Vida and let you know.

mod64 · Post by **mod64** » 04 Dec 2021, 02:56

: Vida recorder data of fuel trim and oxigene sensors

mod64 · Post by **mod64** » 04 Dec 2021, 02:57

mod64 · Post by **mod64** » 04 Dec 2021, 03:01

Idle speed fluctuates a lot now, any clue after seeing the Vida results?

Post by **vtl** » 04 Dec 2021, 07:17

This is a hole somewhere. Smoke it.

mod64 · Post by **mod64** » 04 Dec 2021, 07:21

Ok. Than it must be something with the EVAP or the surge valve connected to that. Will check it. Not sure is smoke is available.