S60 2.4 NA RPM flactuation ? (o2 sensor suspected)
 

Hi there. I am driving S60 2003 year 2.4 NA 140hp with manual transition. The Volvo is with the facelifted ETM (not the problematic Magnet Mareli)

I have the following problem: when I driving with more than 30-40km and switch from gear to neutral very often RPMs start fluctuating between 500 and 1100 and sometimes the car dies. Also when coming to a full stop RPMs drop rapidly to 400-500.

First I suspected the brake booster so I have changed it with a brad new genuine ATE - the problem remains, no change.

I have cheeked for vacuum leaks but everything seems to be fine.

MAF is cleaned and cheked with VIDA seems to work fine.
ETM is also cleaned.

So I started to look at the live data. LTFT is 0.92 which means -8% correction. It means the car running rich of fuel but it does not seems true because there is no detonations in the exhaust, the exhaust pipe is clean and there is no black smoke. (All this characteristics of rich mixture are not fulfilled)

So I relay suspect the front heated o2 sensor. It is still working but seems to be lazy and not very correct. I have uploaded 2 videos. On the first you can see how lazy is the first o2 sensor, there is periods of 2-3 seconds without change of the parameters. As I know it should make changes at least ones a second. I think it also misleads the ECU or just is two slow and the ECU create not perfect mixture. It seems this is the reason for the strange fluctuation of the rear o2 sensor.

What do you think, are those two o2 sensors indicate correctly? And is it possible this to be the reason for my problem?

https://www.youtube.com/watch?v=viY4qg-7EFk

https://www.youtube.com/watch?v=HDHWVaKq2Dc&t=11s

https://www.youtube.com/watch?v=oYdhh-6Wq2o&t=183s

Well... I cured mine (from fluctuating) by cleaning ETM.
Same engine, but 170bhp and on V70.

I know my answer doesn't help much, but at least you know someone reads and thinks..

I would use it as a opportunity to get rid of spare ETM, which I bought unnecessarily, but I don't think you need it..

Maybe someone, someday will.

Miles?

Same engine my front O2 was busted but the idle was stable.

All times when my idle drops when coming at a red light, I pull the hose and clean the butterfly flap on the tb inside and out, especially near the hinges

If the tb was pulled, was the gasket replaced? Same for the intake mani gasket if the pcv was replaced (should be done at about 80k miles)

Side note, was the maf cleaned with the correct stuff? https://www.youtube.com/watch?v=-bejldUOfVs

Don't forget the intake air thermostat on these engines https://www.youtube.com/watch?v=-bejldUOfVs

Maybe also look at the various vacuum hoses attached to the manifold, including the large air duct for cracks

100K miles (160K km). I used the old tb gasket because it seemed ok. I've cleaned MAF and TB with MAF cleaner by Liqui Moly. I am 99% sure that PCV has never been replaced and believe that the intake manifold has never been removed (not absolutely sure). Also I have made the PCV test with the glove on the oil cap and there is no positive pressure in the engine. The glove is slightly sucked.

I forgot to say that I have never had idle problems when the car is not moving and just idle at place. Problem occurs only when switch to neutral and when coming to a stop (again in neutral). This makes me think it is not MAF or ETM related. There is no lack of power or fluctuations when driving on gear or when engine is idling at place. When I drive even with 40-50mk/h the car is under some load. So when I switch to neutral ECU tries to force the car to come into idle. And may be at that point the lazy o2 sensor does not respond fast enough? Sensor is still not busted but may be not that efficient as a new one? I have made a test today - just pulled away the EVAP hose from the intake manifold (in order to simulate a vacuum leak). The results was engine stalls. I believe that o2 sensor have to send immediate info for lean mixture and the ECU has to handle. Am i right?

I have limited knowledge on O2 sensor, but one thing I remember is that is mostly used by the engine when there is acceleration. At steady rpm the engine would not need it to adjust the mixture.

As for the pcv, I would not delay and replace it by now. These typically fail at these miles, and it's better not to wait until they fail - this time it needs a new intake gasket around $20 at Volvo. I only replaced the box itself on my non turbo as the hoses were all in good condition (yet another video on the subject) https://www.youtube.com/watch?v=rRecTJnTJKc

When I removed the tb, I also did reuse the old gasket but coated it on both sides with some O2 safe rtv just to be sure.

Mind you, the manual transmissions fails at the slave cylinder anywhere around your mileage, not sure if this could be related to an idle drop when switching to neutral ? But normally, it starts with loosing some brake fluid https://www.volvoforums.org.uk/archi.../t-131170.html

Thanks for your replays. I am planning to replace the PCV in the summer. I think the EKU takes o2 sensor's readings into consideration as soon as it has reached operating temperature. This is the reason why they build in a heating element - to provide fast and steady operating temperature all the time. It could be transmition related problem because I have some troubles with swithing into first and rear when it's cold. Here I suspect a worn out clutch which I am also going to replace in the summer. It seems that slave cylinder is fine because there is not leaks in the system. I have changed the brake fluid 1 year ago and since then the level is stable without any change.

I had a similar problem and it was in fact the front o2 sensor. Fluctuating idle, near stalls, back fires, flashing cel, surging, etc. Replaced the front o2 and then She purred like a kitten.