02 v70 xc. Rough start but idles fine

[Btrain0517]

So my wife's car has been having this issue lately. It starts really rough like it doesn't want to idle but it will and Itll idle and drive just fine. Only seems to happen on first start of the day. Once the car is warmed up it'll start just fine.

We have a P0422 code but she's had that for over a year now. We never got around to looking into that. Bad O2 sensor maybe.
Any direction on where I should start looking? Thanks all

[a_e_cole]

I just had the same problem start happening today. Took several attempts to get it started eventually it started and had a really rough idle that eventually smoothed out. Drove it, restarted it, every thing seems fine. No codes. Have you figured out the problem? I am suspecting maybe the cam position sensor on mine as a place to start looking.

[draser]

I'd start looking at what the code is, then search this forum. Or google...

[jimmy57]

Rough start cold on dead end fuel system vehicles can be from leaking fuel pump non-return (check) valve or from fuel pressure regulator(FPR) not sealing. Also leaking injectors can be the cause.
The FPR on the mentioned vehicles is integrated into the fuel pump/sender cap that inserts into fuel tank cover.
Leaking fuel injectors can also be the cause.
Usually the fuel pressure loss will cause hot soak in hot weather start issues.
Leaking injectors also cause hot soak start issues from flooding and pressure loss.
The difference between the two is loss of pressure back to tank causes rough running until air is purged from fuel rail but with no black smoke when it starts from tailpipe. Injector leak causes black smoke from flooded cylinder clearing with the same initial seconds of rough running.
Dead end fuel system is one where the fuel goes to rail and has no return line from the engine bay. Fuel leaves the fuel filter and goes forward and doesn't come back, it leaves through injectors only.

Cam postion sensor(CPS) doesn't cause rough running. It is used to associate firing order and once this happens after two crank revolutions and engine starts then it has no effect on running. CPS does get used for variable cam timing on these engines with that feature. Cam timing issues from CPS would be reported quickly and light warning lamps and messages and would not make it run rough only have low power.
On engines w/o CVVT you can unplug CPS once engine is running with no effect. It doesn't need cam and crank synchronization again until it is switched off and started again.