Been dealing with a few rough running issues on my son's 2005 S40 w ~70k miles. First was a vacuum issue so we replaced the oil trap. A few months later it would run fine but pretty brutal rough idle at lights. We changed the plugs, MAF sensor, and the FPS. Still runs fine but after idling for about three minutes it just dies. Any ideas?

 

Codes?
Actual fuel pressure while at idle and higher RPM's?
Good spark?
All injectors firing? Can be checked with Noide lights.
By "vacuum issue" do you mean the PCV system?
It needs to be checked for actual vacuum leaks too.

Martin

 

do you have a check engine light / codes? If not, I'd start by inspecting the tubing from the turbo to the throttle body for cracks leaks (maybe do the starting fluid spray trick?), vacuum line etc. Not sure if the 2005s use the ETM like the S70/80s but if so, that's another problem area. Another possible cause is the cam sensor.

 

The vacuum issue was the PVC. This blog helped me solve that. Was reading a "bank too lean" code before I installed the new FPS. When driving, everything is running smooth and fine. At idle it just stops after a couple minutes. The only code that fires when it stops is random cylinder misfire, just assumed that was from the stall.

 

We are crossing wires...
Vacuum is what the intake/throttle body creates. A broken vacuum line will cause your issues, not the PCV system per say. Unmetered air entering the engine will screw with everything.
What is FPS? Fuel pressure regulator, or?
And a stall wont throw P0300 (multiple misfire)
Martin

 

Sorry, I am a true novice. I replaced the oil trap because of a sucking vacuum sound and loss of power. And I did mean Fuel pressure regulator.

Which Vacuum lines should I check? There is no turbo.

 

The PCV system should "suck", so lost again here I think.
Quick and dirty way of checking for vacuum leaks is to spray brake cleaner, in a very controlled manner, all around the engine where you see any rubber lines around the intake and throttle body. Spray a little, wait. If the engine noise changes, leak. If it doesn't, carry on.
Where are you located at?

Martin

 

The 2004.5 and newer S40s have a Fuel Pressure Sensor, not the old Fuel Pressure Regulator. This is because fuel pressure is handled by voltage changes to the fuel pump. The sensor is located on the pax side of the fuel rail.

I would buy a new Electronic Throttle Control gasket and remove the ETC to clean it. Rough idle is a sign of a dirty ETC.