2004 s40 1.9t DTC codes p0301, 0302, 0303, 0304

[marcpilot1]

Hi! I am new. Hoping to get some insight on what to do next with this ongoing check engine light. The codes that keep coming up after I reset the light are the p0301, p0302, p0303 and p0304. All four cylinders, misfires.
I just installed volvo plugs(8692070), put a new MAF sensor, the fuel pressure regulator was bad so I had to replace that to stop the bucking and kicking and rough idling/running at stops and other conditions while driving. The throttle body has been thoroughly cleaned. No carbon nowhere anymore. No vac leaks that I can find. Sprayed several times all over the place with carb cleaner and stuff trying to find a vac leak. Nothing.
Fuel pressure is 39 to 41 psi. The 02 sensor readings are dropping at least .60 when pushing gas pedal. From what I understand thats what you want your 02 sensor readings or graph to do. And the compression test came back with 195, 200, 196, 201 in cylinders 1, 2, 3 and 4.
The only thing thats going on is the CEL light keeps coming back on after I drive around about 10 miles after resetting the light.
Other than the cel coming on with the same codes, the only other problem is when you drive it, it will cut off at times. Its very very rare that it will do that. But while I'm driving, BAM, it just cuts off. Like, twice yesterday it did it, and that was kind of when I let off the gas with my foot and was going about 30mph, the 2nd time was when I was coming to a stop.
Other than those 2 issues, this s40 with 82000 miles runs great! I love the little car. It runs perfect except the misfire codes and cutting off very, very seldom at times. Sorry such a long post but I wanted to inform you with as much pertinent info as possible. I have more info but I dont want to fill up page after page of all i've done since it started acting up. Thanks for ANY help. I know its somewhat of a mystery! Thx!!

[Livens]

I would start with the coils. Not likely maybe, but both of my coils in my S40 went out within a week of each other... right as it started getting hot last month. In both cases my coils had a fine crack running down the plastic post that connects to the plug. The hot temps were making those cracks spread open further and shorting the spark out to the head.

If you do decide to replace the coils, try the duralast brand at autozone. Around $45 and they usually have OEM Volvo coils in the box! Just shows how much the Dealers mark up the price of parts.

BTW, you didn't mention if the engine is running rough all of the time, or just in certain times, like idling in traffic?

[Vovo_merz]

Yes check your coils and also the wiring for coils that model has a problem of the drying out and cracking especially at the connectors, so if you replaced your spark plugs prior having the misfire issue, you might off triggered it when unplugged it.
please clarify if you had the misfire codes prior doing fuel and spark work or did it happened after