Rough idle leads to near stalling/stumbling

[DUCK01]

I've been searching for a few days, but the responses are overwhelming. I'm hoping that by posting my specific issues y'all can help me narrow the issue down so I don't wind up just throwing dollars and parts at a problem that may be a simple fix.

2004 V40 1.9t with 133,000 miles
I bought the car a couple of months ago to use as a commuter, but know very little about the car's maintenance history.

After a few weeks of ownership, I started getting a flashing CEL under wide open throttle, accompanied by the car physically surging. Some research said this was caused by an active misfire, so I replaced the spark plugs, plug wires, and coils. The repair fixed the problem, or at least enough that I'm no longer getting active misfire codes. The only other thing I've done is mix a bottle of Seafoam with the tank before the current one.

However, I'm still feeling a slight surging at wide open throttle, though it is not enough to throw a code of any sort. At idle (when in gear, like when I'm sitting at a stoplight), the RPMs bounce from about 800-1000, then dip again, then go back up, etc, etc. If I give it a little gas, it'll level out for a second and slowly start the process over again. It hasn't caused a problem until recently. I was first in line at a stoplight and was experiencing the usual RPM fluctuations, but, when I stepped on the gas to accelerate after the light went green, the car didn't want to go and I had to pump the accelerator a couple of times to get the car to start moving. It felt like the car was stalling out. Once I got moving, though, it was fine for the remaining 1 mile to my house. I haven't driven it since then.

The suggestions I've seen online range from cleaning the ICV to replacing the flame trap/PCV systems. In other vehicles I've worked on, the PCV causes low idle issues, but the replacement parts are only $5 and not $250, so I'm hesitant to just jump into that on this Volvo. As for the PCV "dipstick" test, I can feel a little pressure pushing out, but it's nothing like you see on the Youtube videos where smoke is pouring out when the dipstick is removed. I've also seen others say the rough idle may be caused by a vacuum leak or fuel pressure issue. Honestly, I'm stumped.

Oh, and I have a fuel filter, but failed miserably at changing it. I failed to notice the schrader valve on the fuel line and wound up with gas all over my face and chest. Thankfully I always wear safety glasses. I've yet to go back and attempt that, again. Any tips? Do I just depress the schrader valve with a screwdriver to relieve the pressure in the fuel system, or is there some other method? Sorry if it's a dumb question, I'm used to working on Ford trucks - this foreign stuff is baffling to me.

Thanks for any help offered.

DUCK

[cookie77]

Duck,
My 2001 V70 behaves exactly as you described with the bouncing idle and the occasional weak start. Unfortunately i cant offer any advice as I have just started working on my problem. So far just new spark plugs. Ill let you know if I make any progress.

[DUCK01]

I cleaned the ICV this morning and that seemed to solve a lot of the idle issues, at least upon initial test drive. The idle held steady at 700 rpm when the engine was cold and warm, and with the AC off and at full power.

It was a simple job that took maybe 15 minutes. I'll drive some more in a bit and see how it does.

Update:
After more time behind the wheel, this fixed my idle issues.