2000 s70 surging/hesitation (O2 sensor?)

Caberguy · Post by **Caberguy** » 07 Jul 2014, 14:30

I'm starting a new thread as I continue to work this out, as the old one (here:https://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=63952)has gotten a bit cumbersome, and the suspected culprits have changed a bit.

this is an S70 Base with normally aspirated engine, just over 100k miles.

My primary complaint is that the car surges from time to time. Every so often it will feel like it's hesitating, but mostly I feel surging. These surges are generally brief and in clusters, and generally don't feel like the car is going to "take off," though I have had that sensation on a couple of occasions. The idle also feels a bit rough to me, but I've only had the car for about a month and don't really have a baseline for "normal."

The car is also running rich. Both short term and long term fuel trim numbers are trending negative, but still within single digits. I pulled the plugs last week investigating the possibility of a bad coil and found all plugs carbon fouled. I cleaned them and put them back in place.

I've had no error codes at all that weren't a direct result of me disconnecting something.

I've read through the ETM chronicles, and while this might still be the culprit I'm not totally convinced yet, and don't want to just drop the money for a rebuild hoping that it will fix my problem. I'm not having hunting or searching at idle, since I cleaned the ETM a few weeks ago the revs don't drop below idle when I come to a stop. I have occasionally had the "gust of wind" hesitation.

The OEM MAF seems to be reading at spec.

A couple of days ago I replaced the ECT sensor. The old sensor seemed to read a steady 92C without fluctuation once the car warmed up. The new sensor, at the very least, moves around a bit more. I'm not sure yet if this has helped with the rich running problem. But it hasn't noticeably affected the surging/hesitation.

I do suspect a bad upstream O2 sensor, but I'm not sure. Over the last couple of days I've been looking at live data from my upstream O2 sensor and I get a (more or less) sine wave. But the range of the wave seems constricted. The range only extends from about .400v to about .550v. I've read that O2 sensors should cycle between about .1 and .9v. Do you suspect that a failed O2 sensor is the cause of the problem, or is it possible that the constricted wave form is a symptom of a different problem? I should also add that the surging/hesitation doesn't seem to happen until I've been driving for a bit.

Edit: for clarification, when I say the car surges, I mean I feel it surge, not that the revs go up

Caberguy · Post by **Caberguy** » 10 Jul 2014, 19:03

Anything?

I was near the dealership the other day, so I stopped in. Talked to a couple people there who said that 100k miles "is pretty good" for a white label ETM. Also learned that the "software fix" was done in 2009. They wanted $120 just to scan it since there are no error codes (I'm sure that doesn't surprise anybody).

I'm toying with just ordering the Xemodex ETM, it seems like it's inevitable that, even if the ETM isn't causing my current problems, it seems inevitable that it will need to be replaced at some point.

Or just replace, the O2 sensor? I've posted a couple of times about O2 sensor readings but haven't gotten any feedback.

This is the first time I can recall life that I've been hoping for error codes.

I need to get this worked out soon, even if it means spending a bit of money.

Post by **abscate** » 10 Jul 2014, 20:26

I got 11 years and 132000 on my original white label ETM before I replaced it, as another datapoint

Post by **mikealder** » 12 Jul 2014, 02:22

Mine went at 112K Don't read too much in to the software upgrade done in 2009 it mainly widens out the tolerance value before the ECU reports the ETM as faulty. To be honest I always thought the software "fix" was a cheapskate way to try and avoid paying out on warranty claims for ETMs but of course that is a rather cynical view - Mike

Post by **abscate** » 12 Jul 2014, 03:56

I don't know if the new software has ever been de compiled but that view has been shared by many.

Caberguy · Post by **Caberguy** » 12 Jul 2014, 09:48

It seems like everything they did with relationship to the ETM was rather cheapskate.

Caberguy · Post by **Caberguy** » 18 Jul 2014, 15:17

Finally just pulled the plugs again, all very carbon fouled and smelled of fuel. Still running rich after replacing ECT sensor. Replaced the three pronged Beru plugs with single pronged NGK Platinums gapped to .028. We'll see what happens.

Any further ideas?

Any input at all on these O2 sensor readings?

Post by **E Showell** » 18 Jul 2014, 16:35

02 sensors are a maintenance item at 100K miles. Replace both or risk a burned valve down the road.

Caberguy · Post by **Caberguy** » 21 Jul 2014, 11:26

Alright, upstream sensor on the way, hopefully that'll address some of these issues

Caberguy · Post by **Caberguy** » 25 Jul 2014, 11:21

Ok, shiny new Denso upstream O2 sensor installed. Fingers crossed.