Car won't hold idle

[pierremcalpine]

getting slightly frustrated...my 2004 S60 continues to hunt for idle. Goes from 1600 rpm down to 650 until it finally gets annoyed with itself and stalls out. The up and down idle can go on for as long as a couple of minutes.

1) tried cleaning the ETB...no difference
2) Tried replacing the ETB with a touchless version from Xemodex...no difference
3) Replaced the ETB harness all the way back to the ECU...no difference
4) tried unplugging the MAF to see if the car ran any differently...no dice.

Still only getting two CEL's: mirror motor missing & outside air temp sensor low.

I've replaced some of the vacuum lines and don't seem to be getting an air intake leak message any longer...

Oh, and it's also entering limp mode...Lovely.

any ideas?

[Georgeandkira]

"I've replaced some of the vacuum lines and don't seem to be getting an air intake leak message any longer..."

Replace any you missed and look for splits/tears in the larger air handling hoses. If external to the tank, replace the fuel filter.

I just went out to look at my intake manifold. On the right side as you face the engine are 4 tap-offs.

One to the brake booster circuit which features a 2" length of 1/2" ID rubber hose and that oddly contoured Y shaped thing (check valve?). There's an additional small length of hose connected to that Y shaped thing.

One to what I believe is the EVAP control valve under the header panel. It's covered with an abrasion resistant weave.

One supplys vacuum to the incoming air thermostat and is connected to a fine, hard plastic "hose" with a rubber right angle. That rubber angle dries out and crumbles apart. You may have missed it. I use a 2" piece of silicone 4mm hose to replace the one in my last V70 rather than a dealer part. It forms a nice curve and wont kink.
The irony here is that I just found mine completely dried out and broken. I guess I owe you one.

The final one is 12-13mm OD rubber hose about a foot long. It curves right back onto the engine.
Mine is intact but crispy. I'm not touching it before I have a replacement in hand. Check again.

[oragex]

I see it's the 2.4T engine in another topic. May be a vacuum leak, some owners try putting back the old gasket at the intake manifold when they replace the PCV. I see in another thread you are checking the ECU harness, maybe also try to get a MAF from the scrapyard see how it goes as well (some places allow returns for the parts such as KennyUPull which is great because you can try many parts and return them for a credit)

I assume there are no water traces over the CEM plastic cover?

The 2004 also had problems with fuel delivery, an ELM327 adapter with the Torque app can help read the pressure. The FPS and a corroded PEM were the usual suspects.

[pierremcalpine]

Originally Posted by oragex

I see it's the 2.4T engine in another topic. May be a vacuum leak, some owners try putting back the old gasket at the intake manifold when they replace the PCV. I see in another thread you are checking the ECU harness, maybe also try to get a MAF from the scrapyard see how it goes as well (some places allow returns for the parts such as KennyUPull which is great because you can try many parts and return them for a credit)

I assume there are no water traces over the CEM plastic cover?

The 2004 also had problems with fuel delivery, an ELM327 adapter with the Torque app can help read the pressure. The FPS and a corroded PEM were the usual suspects.

Thank you, Orangex. It's actually a 2.5T but not sure that matters. No traces of water over the CEM, tried cleaning the maf and putting back in but no luck.

I too was wondering about the intake gasket but the rough idle is more like a violent surge so I'm thinking it would have to be one heck on an air leak and if it was, would it not also immediately register a vacuum leak?

What is a PEM?

For reference, as I mentioned above this is one heck of a surge in idle. Interestingly, it starts of nice, idling nice and smooth at 1500rpm (it's pretty cold up here right now). It then will go down to 1100 and will still run nicely, it's when it then decides that it's warm enough that the problems begin. it will go down to 600-ish and then seems to realize it's gonna stall itself out so it revs right up to 1600 and then back down to 600 almost stalling, it does this over and over for about 2min. Eventually it stabilizes at 700...but if you press the gas pedal the cycle starts all over again. The more times you force the cycle, the higher the likelihood of a couple of backfires and a stall.

The problem also manifests itself in drive and reverse so if you don't have good mastery of the brake pedal this becomes a real safety hazard.

A part of me just wants to head out for an Italian tune up to see if this helps but I'm waiting for a new power steering reservoir so that I can get the ps system back up to snuff.

I've trolled youtube pretty extensively for good examples of air leaks and I'm almost convinced that this is not a mere air leak - it's just to pronounced and violent.

Please feel free to chime in.

[pierremcalpine]

Thank you GeorgeandKira and orangex for your feedback. Glad I was able to help you find a potential vacuum leak G!

Alright, I finally got to the bottom of this and boy oh boy what a sigh of relief when I started it up and it purred like a kitten. Wow! Brand new car!!!

Alright, first off I just purchased this car from someone who gave up on it and could not figure out the problem. I got it for roughly 300 quid (the car).

As stated previously I started by cleaning and replacing throttle body as the codes pointed me in that direction. The idling became slightly better but was still totally out of whack plus I was still getting misfires and backfires through the intake. I looked around for some vacuum leaks but found that all rubber was in pretty good shape.

I unplugged, plugged, cleaned the MAF, no difference.

Ignoring the fact that the previous owner said they were really good with regular maintenance I finally checked the obvious: sparkplugs. They were totally shot. Gaps were huge. I thought maybe this is it. Nope, limited improvement but same symptoms persisted.

Meanwhile no additional feedback from DICE: just a bunch of misfire codes.

I knew it had an exhaust leak and I was hoping to delay that repair until I figured this issue out first but my neighbors started giving me the evil eye whenever I was working on the car because it just became so darned loud. I have to admit it was driving me nuts as well.

So, off I went to the exhaust shop. I thought I was dealing with one leak at the same upstream of the resonator but the muffler shop found a second major leak just upstream of the flex pipe...AND just downstream of the front oxygen sensor. This got me thinking about whether I might have an o2 issue.

got the car back, it idled much better but still fluctuated and misfired/backfired/stumbled/stalled. Interestingly when started cold it would run fine for about 30s and then start to act up. My research suggested that o2 sensors only begin to work when they reach a certain operating temp so that supported my working theory of an o2 issue.

Got home, read codes again and finally caught a break: "ECM 261A Long-term fuel trim, bank 1 upper limit."

While this did not suggest an o2 sensor issue outright, it certainly pointed in that direction.

Purchased a Bosch o2 sensor slammed it in yesterday and boom, car magically runs as good as new.

So the moral of the story (at least one of them anyway) is to make sure you fix an exhaust issue before continuing your troubleshooting. I'm thinking that the leaks were back enough that the o2 sensors didn't quite know what to make of all this so they did not trigger any error codes until the exhaust issues were dealt with.

I still plan to replace all the vacuum hoses when my order for Chinese silicon hoses comes in.

Wow, I have to say, resolving this issue really brightened my week!

On a side note, I'm afraid that my turbo heat shield suffered a casualty as a result of this mess...I'd love to know who at Volvo chose to put that spring loaded 10mm bolt on the lefthand side of the turbo heatshield. As patient as I was at carefully wiggling that thing back and forth, it crapped out on me and is now held in place by a couple of tie-wraps on one side...not sure that's gonna hold.

[SwissXC90]

Goes to show that regular maintenance is really important

Multiple issues at the same time always make diagnosis much more difficult

Obvious problems (such as your exhaust leaks) are normally quick to spot - one should never delay to get them fix.

Fix small things immediately they happen (exhaust leaks) before other problems start to happen as well, because compound problems cause confounded diagnosis.

[oragex]

That was a smooth issue search and fix