volvo s60 t6 2012 idling bounce

Patrick961 · Post by **Patrick961** » 03 Oct 2025, 02:38

Hello to all
recently i bought a really high spec and well maintaned volvo s60 t6 r design , 2012.
108k miles on it.
A lot of service work done to it to official dealer.
Installed lpg system on it.
all working perfectly.
These last 2 days , when starting cold, after rpm drop to 650, i can hear a idling rpm bouncing around 50 70 rpm from 630 to 700 rpm and a sound coming from the engine like a wave.
NO CEL, or any kind of other symptoms from VIDA .
As soon as engine turn a bit warm the noise goes away.

plugs and coils are new.

(CHECK VIDEO URL PLEASE)

What can it be ?
Thanks to all

Post by **scot850** » 14 Oct 2025, 12:11

Check the throttle body. Just had a random issue with an 07 C30 T5. It had a replacement aftermarket unit fitted, and it was bad from new causing fluctuating idle. No codes were set.

Other issue would be there is an air leak somewhere in the system following the lpg install.

Neil.

Patrick961 · Post by **Patrick961** » 16 Oct 2025, 01:20

tested the lpg system, no problems at all.
the volvo mechanic changed the plastic of the pcv diaphragm because when hot the plastic expanded.
All good.
after days it started again, Randomly doing the fart noise and back to idling bouncing.
open the oil dipstick or oil tap it becomes normal.
Still no error codes.
i want to check the throttle body, but it seems strange again,

Post by **scot850** » 16 Oct 2025, 11:19

If the car goes to normal when opening the oil filler or dipstick, it sounds like a crankcase over pressure problem. The PCV diaphragm is an issue on the newer Volvos with the integrated oil filter and PCV catch tank. I'm not sure if yours is fitted with this or not. I would suggest the PCV system is more likely your issue than the throttle body. I would suggest having the crankcase pressure checked for over pressure or that the system is in line with where it should be. With older Volvos we used to use the rubber/latex glove test by fitting a glove over the oil filler cap and holding in place with elastic bands. Starting the car and see if the glove inflated at idle, and if it just kind of lays flat that is ok, then rev the engine and see if it inflates. If it inflates you need to do a PCV service on your car, if it stays flat or gets slightly sucked in it is ok. Not sure if this simple test is possible on your car or not.

The throttle body will be affected by a PCV blockage issue as it will affect the air flow into the intake.

It may be worth cleaning the throttle body anyway and checking the gasket is not damaged. When cleaning the TB, use TB cleaner only. Do not soak the unit with the spray. I recommend using a cloth sprayed with the cleaner or cotton buds.

Good Luck!

Neil.

Patrick961 · Post by **Patrick961** » 21 Oct 2025, 03:52

i will tell you the solution.
i fixed it, but it was pathetic what i did,
The previous owner that had it,let the bolts of the pcv loose.
all of them. did it the right way, tight them up. good to go. 0 problems...

Post by **scot850** » 27 Oct 2025, 20:43

Well it is always nice when the issue has a nice simple fix! Awesome job.

Neil.