2002 s80 t6 rough idle after driving

richardt905 · Post by **richardt905** » 12 Dec 2014, 15:30

Car starts fine,idle is smooth.After driving short distance and coming to a stop the car shakes and idles rough.When I accelerate it runs smooth..maf cleaned and new plugs also connections cleaned at ecm.Checked for vac leaks but found none...this all started after a short run on the highway, came to a stop off the exit ramp.The car had no power on acceleration, but after shutting it off for a couple hours it was fine....any ideas would be greatly appreciated.

puntmeister · Post by **puntmeister** » 13 Dec 2014, 23:17

I had this same exact issue on my 2002 S80. When first starting (cold engine), idle is fine. Once warmed up a bit, idle is rough - but at speed engine is smooth.

About 95% certain the problem is the oil trap (PCV).

There is an internal diaphragm which, when properly functioning, cuts off the trap when there is excessive suction (which happens to occur at idle....).

If/when the diaphragm ruptures (its just a rubber disc), suction at idle pulls excess air from the crankcase, causing very rough idle.

To check - pull out the oil dipstick. While engine is idling, put your thumb close to the dipstick - if your thumb is sucked into the dipstick, you have diagnosed the problem.

Here is a link to the trap I am talking about (just for reference - you'd want to verify if this is the exact model - I bought mine at a Volvo dealer, for about $65).

http://www.partsgeek.com/y5mfd6k-volvo- ... e+Oil+Trap

Its a pain to replace, as all parts are, but doable. The dealers charge something like $400. Its a $65 part, and takes about 2 hours for a novice.

Post by **oragex** » 15 Dec 2014, 15:22

Isn't it positive pressure when the pcv is clogged? Such as having a glove inflating ?

jbkeene · Post by **jbkeene** » 16 Dec 2014, 06:42

yes, positive pressure

puntmeister · Post by **puntmeister** » 17 Dec 2014, 18:59

I'm not talking about a clogged PCV - I'm talking about a PCV which allows the idle intake suction to pull air through the PCV (from the crank-case).

Kind of the opposite of a clogged PCV - a PCV which should shut off flow to the intake, but doesn't. This happens because a rubber diaghram inside the PCV ruptures.