XC60 T6 - rough idle, mostly while engine is cold
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    1. #1
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      XC60 T6 - rough idle, mostly while engine is cold

      Hello,
      I have problems with my XC60 T6 (Odo ~80k). Car is running on LPG too.
      It idles roughly mostly when cold. When the engine gets warm, it is less protruding. What is more, it registers CEL with random misfires, if is left to idle for 10-15 minutes.
      It's not stalling and I haven't noticed any serious drivability issues.
      The problem does not appear to be fuel related, although misfires are more common on petrol (possibly due to adaptation).
      We have replaced spark plugs.
      I have done a smoke test - replaced intercooler as it appeared to have a leak after traffic accident. Haven't confirmed that there are no vacuum leaks after replacement tho (it's on the list).
      Today we have plugged the car to VIDA - it appears to register missfires when idling mostly on cylinder 5. We have moved around coil packs, but the most of misfires appear in cylinder 5.
      It appears that there is vacuum under oil cap (not really powerful, but you can hear a slight sound once it pops off).
      What is interesting is that once the cap is removed, the it seems that additional air entering through oil cap make the car run better - misfires are no longer registered.
      My mechanic believes the problem could be caused by faulty PCV oil trap, so I have already ordered the part.

      Is faulty oil trap likely to cause such symptoms? Is it possible that, if the PCV diaphragm has failed, the negative intake manifold pressure is directed to top cover causing vacuum in it?
      Has anybody had problems with oil traps? I have read that they recommend to replace them routinely.

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    3. #2
      It could be several things. At your mileage, it is due for spark plug replacement if that hasn’t been done already. It could be the pcv/ oil trap. It could be a failing 02 sensor. My first thought, however, is it could be moisture buildup in the gas tank, which is a very common source of misfire issues. People tend to throw a lot of money replacing hardware when often times a $3 bottle of “dry gas” like the yellow HEET in a fresh tank of gas will be enough to disperse that moisture. You might need to run a couple of tanks of gas (one bottle of HEET per tank) to realize the full benefit but if it’s a fuel contamination issue you should feel the benefits almost immediately. One of my mechanic friends taught me this trick years ago and I’ve probably fixed misfires on about 10 cars with HEET since then. Try that first, because no hardware replacement will help if the problem is actually a fuel quality issue. Avoid sketchy gas stations and letting your car sit with a nearly empty tank, as poorly maintained gas stations tend to have more issues with water building up in their fuel supply, and more condensation can build up in your tank if it sits with little fuel and lots of air space.
      2011 S60 T6 with Polestar tune+TDI-Tuning : KW V3 coilovers : DO88 fmic : Ferrita downpipe : Powerflex "race" torque mount insert
      12.99 at 109mph

    4. #3
      It could be several things. At your mileage, it is due for spark plug replacement if that hasn’t been done already. It could be the pcv/ oil trap. It could be a failing 02 sensor. My first thought, however, is it could be moisture buildup in the gas tank, which is a very common source of misfire issues. People tend to throw a lot of money replacing hardware when often times a $3 bottle of “dry gas” like the yellow HEET in a fresh tank of gas will be enough to disperse that moisture. You might need to run a couple of tanks of gas (one bottle of HEET per tank) to realize the full benefit but if it’s a fuel contamination issue you should feel the benefits almost immediately. One of my mechanic friends taught me this trick years ago and I’ve probably fixed misfires on about 10 cars with HEET since then. Try that first, because no hardware replacement will help if the problem is actually a fuel quality issue. Avoid sketchy gas stations and letting your car sit with a nearly empty tank, as poorly maintained gas stations tend to have more issues with water building up in their fuel supply, and more condensation can build up in your tank if it sits with little fuel and lots of air space.
      2011 S60 T6 with Polestar tune+TDI-Tuning : KW V3 coilovers : DO88 fmic : Ferrita downpipe : Powerflex "race" torque mount insert
      12.99 at 109mph

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    6. #4
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      SO it is running rough on LP and on gasoline. That it runs rough on LP takes away fuel related issues.
      The vacuum when removing oil cap is almost certainly the breather box on top of valve cover. That assembly has a crankcase pressure regulator diaphrgm that controls crankcase venting. If it fails the port to the holes in each intake port for oil vapor evacuation will be the source of the vacuum and that could cause rough running on either fuel type.
      That you can ID a cylinder is a problem though. You may have a fouled plug as the port from breather starts at cyl 6 and the most oil will go to 6 then 5 then 4 etc. These engines have some tendency towards valve deposits on exhaust valve seats if not run aggressively periodically. Gearing to down and driving at 4000 rpm + for a couple of minutes or more will often take care of the deposits as that will rotate valves. Low engine speeds often do not create the spring wrap and tappet rotation that makes valves rotate and the rotation as valve closes offers cleaning action.
      2004 V70R GT 255K miles purchased 9/15/12. Had several R company cars in the past and had to have one of my own.
      OBX DP but I've only just begun.............
      2010 XC60 T6 RD
      Several farm trucks, tractors, trailers, and a Suzuki Carry Kei truck.

    7. #5
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      Quote Originally Posted by cattlecar View Post
      SO it is running rough on LP and on gasoline. That it runs rough on LP takes away fuel related issues.
      The vacuum when removing oil cap is almost certainly the breather box on top of valve cover. That assembly has a crankcase pressure regulator diaphrgm that controls crankcase venting. If it fails the port to the holes in each intake port for oil vapor evacuation will be the source of the vacuum and that could cause rough running on either fuel type.
      That you can ID a cylinder is a problem though. You may have a fouled plug as the port from breather starts at cyl 6 and the most oil will go to 6 then 5 then 4 etc. These engines have some tendency towards valve deposits on exhaust valve seats if not run aggressively periodically. Gearing to down and driving at 4000 rpm + for a couple of minutes or more will often take care of the deposits as that will rotate valves. Low engine speeds often do not create the spring wrap and tappet rotation that makes valves rotate and the rotation as valve closes offers cleaning action.
      Thanks Bunnspeed and cattlecar for your extensive input!
      I can't easily figure out what could be the cause. The problem is mostly prevalent when the engine is cold - it misfires on both petrol and LPG. Once it gets warmer, it seems to misfire more on petrol. I have already added injector cleaner to the gas tank and plan to run a few tanks of petrol to keep the injectors working - it is possible that they may get dirty as they are used only occasionally, and most of our trips are short. Great point about the moisture in the gas tank - will consider adding some equivalent product available in Europe on the next full tank.

      Cattlecar - I have read a lot about oil traps. It seems that vacuum should be present in most petrol engines, and nearly non existent in diesel engines. So I am yet not sure if vacuum present in my engine is extraordinary. Anyway, it is probably worth replacing just to rule out this potential cause. Spark plugs are already replaced. It seems that I can ID cylinder only when the car is running on petrol, that's why I am thinking that dirty injector could also contribute to the problem. On LPG the misfires are more or less random. What effect would the deposits on the exhaust valve cause? Lower compression and thus misfires? I assume that LPG is cleaner and hotter running fuel which potentially could keep the valves cleaner. What is more, it is also known to cause valve seat recession - I am just hoping that this is not the case.

      Another question for enthusiasts. Snapshot from VIDA included - if your car idles, does it have "Air bypass valve" Closed? In my case, it is always closed. I tried to disconnect MAF to rule out it as a potential cause for rough idle - strangely, it appeared to react to idle condition as I suppose it should - Open, when idling, and Closed when RPM get higher. What is more, my MAF seems to get readings on idle from ~2 to 6 g/s depending on the engine temperature. I suppose all air intake is MAF+EVAP?



      Thanks for bearing with me It is fun to share experience with others in trying to get the engine ticking perfectly again

    8. #6
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      The air bypass valve is a valve on the turbo that is there to vent the pressure from turbo outlet back to inlet to stop the pressure from going backwards through compressor housing. It is not a cause of rough idle. Valve recession is certainly possible and is found through compression check. Valve deposits are less likely on LP but if the engine is not run hard they will not be cleaned off.
      Compression check is the best thing to determine if that is the problem before any money is wasted on things that do not contribute to the repair.
      Crankcase should not have any noticeable vacuum when oil cap is removed. A vacuum gauge can be easily attached to oil dipstick tube as a hose on the gauge of the correct size will slide inside that tube and the pressure(vacuum) can be monitored. The crankcase vacuum should not be more than 2 inches or -7 kPa, it is usually half this value.
      2004 V70R GT 255K miles purchased 9/15/12. Had several R company cars in the past and had to have one of my own.
      OBX DP but I've only just begun.............
      2010 XC60 T6 RD
      Several farm trucks, tractors, trailers, and a Suzuki Carry Kei truck.

    9. #7
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      Quote Originally Posted by cattlecar View Post
      The air bypass valve is a valve on the turbo that is there to vent the pressure from turbo outlet back to inlet to stop the pressure from going backwards through compressor housing. It is not a cause of rough idle. Valve recession is certainly possible and is found through compression check. Valve deposits are less likely on LP but if the engine is not run hard they will not be cleaned off.
      Compression check is the best thing to determine if that is the problem before any money is wasted on things that do not contribute to the repair.
      Crankcase should not have any noticeable vacuum when oil cap is removed. A vacuum gauge can be easily attached to oil dipstick tube as a hose on the gauge of the correct size will slide inside that tube and the pressure(vacuum) can be monitored. The crankcase vacuum should not be more than 2 inches or -7 kPa, it is usually half this value.
      So the next coming steps will possibly be as follows:
      * Fuel tank anti-freezer
      * Oil trap replacement
      * Compression check
      * Possibly cleaning MAF, not sure if it makes sense to clean throttle body, idle control valve

      Somehow I would want to believe that the compression is fine, because misfires somehow seem not to happen always in the same fashion (depend on the weather (humidity)?). What is more, the engine starts perfectly even in freezing temperatures, revs up 1500 and falls to 600s in a minute or so, and that's then the idle play begins. One day the engine decided to idle @700s and there were no noticeable misfires (strange) Am I right to think that if any coil is failing or is about to fail, it should be constant, and not dependent on the rpm? Also, if this is compression problem, the misfires should also point more of less to one or a few cylinders despite fuel?
      I have been scratching my head for weeks with this It's a pity that Volvo didn't split the exhaust manifold into banks - that would help with diagnostic process.
      Anyway, I will keep the thread updated about how the story unfolds.

    10. #8
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      Quote Originally Posted by cattlecar View Post
      The air bypass valve is a valve on the turbo that is there to vent the pressure from turbo outlet back to inlet to stop the pressure from going backwards through compressor housing. It is not a cause of rough idle. Valve recession is certainly possible and is found through compression check. Valve deposits are less likely on LP but if the engine is not run hard they will not be cleaned off.
      Compression check is the best thing to determine if that is the problem before any money is wasted on things that do not contribute to the repair.
      Crankcase should not have any noticeable vacuum when oil cap is removed. A vacuum gauge can be easily attached to oil dipstick tube as a hose on the gauge of the correct size will slide inside that tube and the pressure(vacuum) can be monitored. The crankcase vacuum should not be more than 2 inches or -7 kPa, it is usually half this value.
      Update. I have replaced oil trap and remeasured compression. The compression appears to be fine, within acceptable range (130-145 psi).
      Replacing oil trap didn't fix the problem. The rough idling persists.
      Not sure what is the major contributing factor. The idling is only present with low RPMs, if the engine is revved, there is no noticeable misfiring. I was thinking of problems with throttle body or idle control valve, but there is no dip of RPMs when throttle is closed.

      Several inquiries:
      1) Could it be because of faulty coil packs, with inconsistent misfires, and mostly when idling? I plan to move them around and to verify with VIDA if misfires move around. I believe misbehaving coil packs should give problems with higher RPMs too?
      2) Will probably have to smoke test air intake system once again.

      Somehow I would tend to think that the problem is related to air/fuel mixture, but STFT/LTFT are within acceptable ranges.

    11. #9
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      Some live data:
      https://files.anuzis.lt/d1dec80a2b.mp4
      Is it normal for ignition advance to bounce this roughly? Is it a result of misfire? It is only present when car is idling. If I rev it, ignition advance is stable and no misfires are registered.

      As the car fuel is bifuel, when warm, it seems to misfire mostly in one cylinder on Petrol. Comparing live data using Petrol and LPG, ECU wants to lean the mixture when run on LPG, and enrichen it with Petrol. I have moved around the coil packs - when engine is warm, the misfire persists in cylinder 5. I believe petrol injectors are also worth checking for any possible blockages, as it may also contribute to misfires when idling?

    12. #10
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      Ignition voltage is lower idling so coil issues are unlikely.
      Ignition timing is used as an additional way to stabilize idle speed.
      Injector problem is not impossible but is not anything I have seen on this engine.
      I have zero experience with LPG on these engines so I can't spek to any issues that arise, if any, from its use. I do know that engines using gaseous fuel need harder valves and valve seats or increased wear results. I do not know for sure that the B6304T2 in that car has the hardened parts but I believe it does as a result of issues Volvo had with some engines in the mid 2000's. If I were working on this car I would be pulling the intake manifold back and viewing inlet valves for deposits. Deposits on the valves disturbs the fuel mixing and causes cylinder specific idle problems. Once you go above idle speed the airflow increase overcomes the issue. If one vale set is heavy with deposits that can be due to spray issues with injector. You may see a pristine clean spot on side of the port area and the rest is soiled. The normal situation is to have pretty clean valves and ports deeper into head with some slight soiling further out where fuel spray does not wash. The intake is easy to remove. The only tough part is the fuel rail connection. There is no easy way to check the injectors for poor spray pattern on that engine. If it had two banks the fuel trim numbers could be viewed for the two cylinder groups as an indicator of injector issues. Turbo versions use one front sensor and control all injectors in one cluster. If injectors are suspect the usual way to determine if that is the cause is to exchange the injector with one from another cylinder and see if the problem changes cylinders.
      The mixture changes you mentioned are normal for short term fuel trim. Long term fuel trim, idling should be viewed after 12 minutes of idling. If you change from LP to gasoline there will be short term fuel trim jumps.
      Is the LP system an add-on system or is it Volvo factory equipment? Volvo had dual fuel vehicles but I can't recall ever seeing that equipment shown for the B6304Tx engines when I view parts catalog.
      Last edited by cattlecar; 05-02-2019 at 08:52 AM.
      2004 V70R GT 255K miles purchased 9/15/12. Had several R company cars in the past and had to have one of my own.
      OBX DP but I've only just begun.............
      2010 XC60 T6 RD
      Several farm trucks, tractors, trailers, and a Suzuki Carry Kei truck.

    13. #11
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      Quote Originally Posted by cattlecar View Post
      Ignition voltage is lower idling so coil issues are unlikely.
      Ignition timing is used as an additional way to stabilize idle speed.
      Injector problem is not impossible but is not anything I have seen on this engine.
      I have zero experience with LPG on these engines so I can't spek to any issues that arise, if any, from its use. I do know that engines using gaseous fuel need harder valves and valve seats or increased wear results. I do not know for sure that the B6304T2 in that car has the hardened parts but I believe it does as a result of issues Volvo had with some engines in the mid 2000's. If I were working on this car I would be pulling the intake manifold back and viewing inlet valves for deposits. Deposits on the valves disturbs the fuel mixing and causes cylinder specific idle problems. Once you go above idle speed the airflow increase overcomes the issue. If one vale set is heavy with deposits that can be due to spray issues with injector. You may see a pristine clean spot on side of the port area and the rest is soiled. The normal situation is to have pretty clean valves and ports deeper into head with some slight soiling further out where fuel spray does not wash. The intake is easy to remove. The only tough part is the fuel rail connection. There is no easy way to check the injectors for poor spray pattern on that engine. If it had two banks the fuel trim numbers could be viewed for the two cylinder groups as an indicator of injector issues. Turbo versions use one front sensor and control all injectors in one cluster. If injectors are suspect the usual way to determine if that is the cause is to exchange the injector with one from another cylinder and see if the problem changes cylinders.
      The mixture changes you mentioned are normal for short term fuel trim. Long term fuel trim, idling should be viewed after 12 minutes of idling. If you change from LP to gasoline there will be short term fuel trim jumps.
      Is the LP system an add-on system or is it Volvo factory equipment? Volvo had dual fuel vehicles but I can't recall ever seeing that equipment shown for the B6304Tx engines when I view parts catalog.
      Could you have a look at this VIDA readout:


      What makes me worried is that ECU is actively managing ignition angle despite engine running steadily - no significant drops in RPMs, just intermittent misfires. I am wondering whether the ECU could be actively falsely managing ignition timing and thus causing the misfires itself. When the car is started, the car revs to 1500 rpms and idles steadily until it falls to regular idling speed @~600 rpms. I assume ignition timing is mostly influenced by knock sensor? Could it be the cause for the symptoms? Is there any way to check it with VIDA or does it require replacement? As I am just an enthusiastic car driver, I haven't plugged this diagnostic tool to any other Volvo. I wonder if it is normal behavior for ignition angle management to be this erratic, if, for example, there is a known reason for misfire (ex. vacuum leak, coil failure etc).

      LPGs was installed as an add-on. I think it was never an option in any of the modern Volvos. I think SAABs used to have models with LPG from factory.

      Point noted regarding intake valves. I think intake manifold will be the first strip down then once any possible electronic component failure will be ruled out.

      It's really a pity that all the cylinders are on a single bank - it doesn't help in diagnosing the problem.

      Is it complicated to remove fuel rail and move fuel injectors around? As it may not be a problem in regular car, as this is driven with LPG, petrol injectors are used probably 10% of the engine running time, so I assume fuel injection related problems are much more likely.

      Regarding fuel trims - I was just assuming that if LPG system is running engine rich and after driving for an hour you stop the engine and leave it overnight. Next day you start the engine cold in open loop operation with petrol, ECU has its adaptation table that the car was running rich and leans the mixture, so, if there are additionally problems with petrol supply (ex. blockages of injectors), they might be exacerbated. Despite it possibly sounding logical, I don't think this is the case - I tried to run the car only on petrol for longer period of time without any noticeable positive effect.
      Last edited by flyeris; 05-02-2019 at 02:35 PM.

    14. #12
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      Knock sensor control is not the source of that ignition change. The knock sensor range is less and would be stepped in 3 degree increments. I have seen the ignition do the rapid changes when the engine is idling rough. Idle speed control through throttle is too slow. If you put it in and out of Drive or Reverse you will see a swing of the ignition timing used to counter RPM drop.

      I guess the fuel trims due to LP use is the cause. On an add-on system I'm unsure if the ECM is stopping fuel trim adjustment.
      2004 V70R GT 255K miles purchased 9/15/12. Had several R company cars in the past and had to have one of my own.
      OBX DP but I've only just begun.............
      2010 XC60 T6 RD
      Several farm trucks, tractors, trailers, and a Suzuki Carry Kei truck.

    15. #13
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      Ok, thanks, point noted regarding knock sensor involvement in ignition management.
      I don't think that fuel trims is the cause. I have tried to run car for extended periods on petrol only to eliminate adaptation as a cause, and the misfires persist. So it must be something different.
      Should vacuum leak always come with elevated short term fuel trims?
      Tomorrow I will bring car to the third specialist - we will see if he possibly has any new valuable insights.

    16. #14
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      I just wanted to ask whether you found the reason for the rough idle.
      I have a similar problem with a V70 T6 which is also LPG converted.
      I already changed PCV, spark plugs and ignition coils but it is still there.

      Thanks in advance.

      Quote Originally Posted by flyeris View Post
      Ok, thanks, point noted regarding knock sensor involvement in ignition management.
      I don't think that fuel trims is the cause. I have tried to run car for extended periods on petrol only to eliminate adaptation as a cause, and the misfires persist. So it must be something different.
      Should vacuum leak always come with elevated short term fuel trims?
      Tomorrow I will bring car to the third specialist - we will see if he possibly has any new valuable insights.

    17. #15
      Junior Member nielssc's Avatar
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      Did you found the reason for your problem?
      I have a similar situation with a 2012 Volvo V70 T6 Polestar LPG.
      I already changed the PCV, the spark plugs and the ignition coils. No engine light or fault code.

    18. #16
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      This sounds like it could be many problems. The first thing I would do is replace your spark plugs, if that hasn't been done yet. If that doesn't fix it, I would check the ignition coils on the cylinder it says that it misfires on. If you swap that coil to a different cylinder, and then that cylinder misfires, its your coil. If its clearly not the coil, I would replace/clean out either the oil trap as an assembly, or just replace the circle cap part that is on it, spring, and rubber gasket included. If there is also a rough idle felt within the cabin of the car, I would check the engine mounts. This next one is just a reccomendation, and its a universal thing throughout all cars, you could remove your throttle body, and clean it out.

    19. #17
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      I have the same situation. Does anybody find the problem?

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