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Discussion Starter · #1 ·
The patient is S80 3.0 T6 (304hp) 2012 inscription with approx 230k miles on it which is actually for sale. I'm thinking about buying it as it has full service history etc.however the engine is rattling/shaking when driving with constant speed (i.e. on Cruise Control), it's especially easy to feel when driving slow 30-40mph. It feels like the engine has misfire or something but there are no errors on board computer, no check engine, no errors in VIDA. Any clues what to check before buying it?

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The issue is that it could be many things. Assuming there isn't a mechanical issue with the engine/fuel/ignition system, the first thing in my mind is engine mounts. That being said, if you can dive deeper and see the actual misfire counts, I would start there. Even though the car isn't throwing any codes, it could still have a misfire. Generally the car won't throw a code until a certain misfire threshold is met. Looking at the misfire data will which cylinders, if any, are misfiring. Do the same for fuel injectors. From there maybe look at a possible driveline issue. While not commonly mentioned, if the car is AWD it could certainly be a driveshaft issue especially with that high of mileage. Same goes for all 4 axles, if one is faulty in some way you could certainly have a vibration issue. Look at the rims and see if any of them are significantly out of round. Have the balance check on all 4 wheels as well. Lift the car and check all suspension parts by feeling for play in the wheels. You definitely need to get to the bottom of this before you buy the car. If the seller is willing to allow it, bring it into a shop and have them take a look. A diagnostic fee is well worth it to save yourself from buying a car with a major issue.
 

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If there is no misfiring, the rattling and shaking may be due to worn motor mounts or upper engine torque rod. In my experience, a misfire will usually affect power with a noticeable stutter. Whereas, worn mounts cause increasing vibrations or rattling at certain rpm’s. The upper torque rod and engine mount are fairly easy to replace. Not so sure about the lower mount.
 

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Discussion Starter · #4 ·
First of all the issue happens only when the engine is warm, no issues when it's cold.
I've checked missfires in ECM:
-misfire counter emission related, total -> 132
-misfire counter cylinder 1 -> 0
-misfire counter cylinder 2 -> 0
-misfire counter cylinder 3 -> 0
-misfire counter cylinder 4 -> 0
-misfire counter cylinder 5 -> 0
-misfire counter cylinder 6 -> 0

Fuel rail pressure and fuel pressure are fine (according to the VIDA).
The wheels was balanced and also changed with another set. There are no Volvo specialised garages around me so I want to check it by myself as much as I can. It's pretty weird that the issue occurs only when engine is warm.

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