I read a lot about idling problems on Volvo cars but I think this kind of problem is a little bit different.

This same problem concerns two (mine and my father's) European S40 engines B4184S11 with about 70k km.

The idle generally works fine when the car is not moving having about 800rpm. The problem comes when the car is moving and I set the gear to empty (no gear set). The rpm indicator is moving progressively almost down to zero and sometimes the engine goes off and other times at the edge of the 0rpm takes a deep breath and fluctuates between 1000rpm and 0rpm until it gets steady to normal idle (800rpm) keeping the engine on.

I checked the hoses for leaks and I found nothing. I measured the solenoid vacuum resistance and I get values (not opened circuit). I cleaned the electronic throttle as well as the MAP sensor. Nothing changed. PCV hose is connected with the valve without any further check ie valve itself since the check is done without disassembling the manifold.
O2 sensor is not checked at all.

Any ideas?

 

Did you scan for any stored OBD2 codes? did you spray some carb cleaner around to check for air leaks? A smoke test may be needed to find some of the more hidden spots. Any signs/sounds of an exhaust leak? I wouldn't suspect the O2 sensor as that would likely throw a code. A few things I'd check 1) fuel pressure (possibly a wonky pressure sensor/pressure regulator (if you can even has a regulator) 2) worn or fouled plugs (pop one out to see if its oily or black vs gray/tan. 3) smoke test for intake air leaks 4) test the PCV / crankcase pressure (you can try the "surgeons glove" trick). After that, it would be time to pay a properly equipped shop for some diagnostics (ie using VIDA/DICE etc to collect run time data).

 

Hi, thank you for your reply.

Concerning my car, I get a few weeks now a P0171 ODBII Code (system too lean with Long Term Fuel Trims (LTFT) about +19% that decreasing progressively around +%10 when RPMs are increasing ie 2.500RPM), but the problem with the idle was months before the CEL light gets on. From the other side of my father's car, there is no ODBII error but it has the same idle behavior.

1) I don't know where the fuel pressure is located 2) I will do it. What does black or gray/tan mean? 3) I show some videos but am unsure if I can do it, anyway 4) What am I looking for with the pressure test?

Yes I have to visit a technician but I am on vacation this month, thanks.

My engine is B4184S11 and looks like this (this is not my photo you can see more photos of the engine here https://volvoforums.com/forum/volvo-...r-code-100355/)

 

If you found a lean fuel trim code then you probably don't need to check the plugs. My mention of colors was that you can look at the plugs to get some insights into how things are burning. ie a weak spark or rich fuel mix will leave carbon or oil on the plugs - a lean fuel mix will burn hot so that would burn off any carbon/oil and may leave a glazing (of melted deposits) or even show some melting/pitting of the electrode on the plug. light gray/tan with no other issues as noted means the plugs are doing their job and is considered "optimal". Its also possible other sensors are in play like the ECT (coolant temp sensor), MAP, possibly the front O2 sensor but generally I'd expect other symptoms like a wandering temp guage or other codes. Curious what fuel you run. As an easy tune, fill up with a name brand premium fuel. The major brands include extra detergents and a couple of tankfuls can clean up the injectors (or throw a can of Techron in the tank).