S40 1.9t rough idle.
 

After it sits in park running for about 20 min or so it gets pretty bad. At that point I shut off the engine. Then restart it and it will barley stay running. I have replaced plugs, wires, coils, file filter and no better. Runs fine while driving. Any ideas?

Any other symptoms? ie does the temp gauge do anything funny (like wandering up) or does the fan stay on for an extended period? If so you may have a bad temp sensor (the one under the thermostat. Does it have extended cranking when cold? (may be a leakly fuel pressure regulator - you can pop off its vacuum line and see if any gas drips out). Any check engine codes? (the OBD2 scan port is under the drivers side of the console above the gas pedal). Did you look around for any vacuum or air leaks?

Temp gage is steady and fan runs normal. No check engine light. No obvious vacuum leak. I will check for leaking fule regulator. Thanks.

It would be a good thing to be able to check your fuel pressure. You can most likely borrow a fuel pressure gauge from the local autoparts store like Autozone - for free. Or you can buy one on the cheap from Harbor Freight (nice to have one of these).

Or even better, check out the smartphone apps that work with a Bluetooth OBD "dongle", giving you a HUGE amount of valuable troubleshooting info. For example, using the Torque Pro app (an upgraded version of the excellent free Torque app) and a cheap Bluetooth OBD dongle, I can monitor not only my V50's fuel pressure, vacuum (and boost if it's a T5), coolant temperature, timing advance, etc., but can pull up graphs showing the O2 sensor readings and fuel trim values, both of which can help pinpoint the problem. And the total financial outlay will be in the $20 range - you can't beat that!

Any idea what my fule pressure is supposed to be. It's a 2004 s40 1.9 turbo

On my 2.4i, it's 55psi. Don't know if it's different on a 1.9T.

I really wish the Volvo manual was a "normal one"... it used to take me seconds to look up specs on my Acura (.pdf manual). With the Vida approach, it's a royal PITA to look up "simple stuff'...

the 1.9s use a fuel pressure regulator vs the pressure sensor design (which can control the pump's pressure). I believe the PSIs for the 1.9T is around 45.. Usually the symptoms for a bad FPR on the 1.9Ts is extended cranking at a cold start. The regulator has a vacuum diaphram in it which tears and allows the rail to lose PSIs over night. A common trick is to pull off the vacuum host and if you see gas come out, the FPR is bad. The testing for the fuel pressure is to make sure your pump in not about to give up the ghost. Thought here is as the pump heats up, the motor loses effectiveness. This can mean its drawing too much current or or not holding the PSIs in a warm engine.

Fule pressure is only 35psi. When I ramp up the rpms it hits 40 for a second and back to 35. 45 psi is what it should be. FOR ???

Sorry, FPR ???

FPR = fuel pressure regulator - the little gizmo that plugs into the drivers side of the fuel rail

According to the Haynes manual, the regulated fuel pressure should be 44 PSI (3.0 Bar) and the unregulated delivery pressure from the pump should be between 70 and 116 PSI.

Seeing you measured 35 PSI, you may have an issue with the fuel pump relay, the pump or the regulator.

Replaced the FPR. Fule pressure is right on now. But I'm still having the same issue with rough idle.

rough idle could be intake air leaks, dirty MAF, throttle body etc.

I have the exact same car, 2004 S40 1.9T and I also had a rough idle. I went to my mechanic and he watched the engine as I revved it up a few times and he found it. Look at this post. Look at that hose on your car and give it a good squeeze to see for any cracks or holes in it. My mechanic gave it a squeeze and it broke into 2 pieces in his hand and it wasn't like rubber anymore, it was more like plastic. He replaced it with a random hose he had in his shop and some hose clamps, but it was kinking after a while, so I just bought the OEM hose on FCPEuro for 12 bucks when I was ordering some brake pads anyway. Took 5 minutes to get on and it works fine now.