Non consistent misfire - sorry for the long details
 

Bought the V40 6 months ago. Car ran great. After a few months CEL popped up with O2 sensor bank 1 sensor 1. Car still ran great. Light would come and go. A month ago I drove to work fine. When I fired up to go home, ran like garbage - misfire and hesitation. Went straight to O'Reilly to code it. Had a cylinder 2 misfire, and the O2 code. Bought new OEM Bosch plugs and wires. Still missing. Obviously new(er) coil on Cyl 1 and 4, original blue and grey coil on 2 and 3. Replaced coil on 2 and 3. Ran great for a few days, CEL went away. Out of the blue, the misfire is back. CEL same, Cyl 2 misfire and O2. Replaced upstream O2 sensor, ran fine for a day or 2, misfire back. Some days it runs okay, some days it misfires. Checked wires leading to coils, they're good. MAF is clean as a bell. All plugs clean, dry, and free of carbon burns. Pulled injector wires while running, obvious shudder as expected on each one when removed. Turbo sounds great, spools up great. Car runs like trash now most of the time, but every now and then it runs absolutely fine. New timing belt and water pump, new oil and filter, new engine seals to treat original oil leak. 120k miles. Don't have the money to pay a Volvo dealer $400 for "diagnostic" (guess work) and I'm now at an absolute loss of ideas. I really need help. Forum/Google/Bing/Shadetree Mechanic searches yield nothing.

I'm gonna try not to let the sting of you calling my work, as a shop technician, "guess work" and assume you haven't spent $5-10k on diagnostic and testing equipment while I try to help you.

I would start by plugging in my $2k scan tool, start the car and monitor cylinder activity. Noting any deviation from spec and hope the problem presents itself in a timely manner so I can make money on the fraction of $400 diagnostic that you paid for (about $50)... usually not. Cars with intermittent problems always come in on their good days. But I'm guessing you don't have a scan tool, so...

(I'm laughing and meant the above in a sarcastic way and hope you laugh too.)

I'll run thru my check list and assume nothing odd was found or corrected until I'm out of ideas. If something is found clear the code and run it a few days to see if it pops back up.

Why do misfires happen? Too much air or fuel, not enough air or fuel, no spark, no compression or nowhere for the exhaust to go. So where to begin? The code, you said, was pointing to cylinder 2 and not the others I would skip air/fuel mix and exhaust and focus on spark and compression. I would 1st check the gap on the plug to make sure it was correct. They usually come pre-gapped but errors do happen. Also check the whole plug for abnormalities. Micro cracks in the ceramic can cause problems. Always torque spark plugs to the recommended spec. Swap ignition packs and see if the code moves to the other cylinder. If you have a multimeter check the wire resistance to make sure it's in spec also. Next I would do a compression test. Kits can be bought at an auto parts store for $20-50 just make them verify it will work on your specific car and that they will take it back if it doesn't. Make sure compression is in spec. It's a good idea to check these things on all cylinders. It's my day off and I'm drunk so unless I missed something, from there it moves to air/ fuel intake or exhaust. That it's localized to one cylinder tells me not so much but it wouldn't hurt to recheck the fuel injector.

Report back with your findings and we can go from there.

Good luck and be safe.

My "guess work" comment was a joke or sarcasm also. I respect the professionals very much, just can't afford them. Putting a new mass airflow on as we speak

So with me MAF sensor, fired up the car and it would t even stay running. Just starved out and died. Unplug me MAF sensor, start car and it runs with the same old misfire again. Plug MAF sensor in while car running, car stays running this time but still runs like total trash. Paid $3k for the car and between all the tune up, parts, oil leak and everything I'm in it for over $4k now... Do I set it on fire and start over? I'm seriously lost. My dad was a mechanic most of his life and I wish he were around now, but I'm in it now so please, if you have any solid, preferably inexpensive fixes I can try, I'm all ears...

I was hoping that was the case and I wasn't just coming across as an ass. I often have to remind myself that nobody wants to bring their car to a shop and they are never happy that they do.

After the sarcasm I did try to point out things I would look at. Did you try them?

So the plot thickens. Cylinder misfire has vanished (code wise) and now only a MAF code exists. P0102. With a brand new factory MAF sensor on it, it runs like crap. With it unplugged, runs like crap. Idle is smooth with a very occasional light hiccup. Once in gear, skips increase in frequency and intensity. If I accelerate at a slow and I mean slow rate, it runs okay, if I get in it at all it misses badly. Checked IACV, functions properly. I do not have a multimeter to check any curents or loads on wiring, nor would I know what I'm looking for. Do not own a compression tester, but I don't believe this is the issue. Exhaust has no fuel smell and has plenty of force. Read that a notorius vacuum leak could be to blame behind the PS pump, but all hoses under there look fantastic. At this point... I am still at a loss and with wife on my back, not sure where to go from here. Will try to scratch some cash together for full, professional dignostic testing I suppose...

double check the "factory MAF" part number- not all replacement parts work for all models - you may need to research the specific OEM number for your VIN.

Good call. Will check it out for sure. So frustrated. Ran the AC on the way home and the car ran great. Didn't skip other than at startup. Then went back out this evening, ran AC, car skipped again. Grrrrr