S40 T5 awd 6spd manual. Started having a miss. Changed plugs to irridium Autolites about 10 K ago. Tried new NGK irridiums now. Check engine light is just flashing and reader shows pending codes P0300 thru P0305. Clearing the codes miss goes away. Rev car up to 2500 ish rpm and miss starts again and back off to idle miss stays. Shut the car off and restart and miss is gone til revved to 2500. If i restart it the miss is gone as long as I keep it under 2500 rpm. So tried disconnecting coils 1 at a time and #2 isn't firing. Swapped coils from 1 to 2 but miss stays at #2. Disconnect #2 fuel injector and it makes no difference on engine running.
Disconnected MAF and makes no difference . If it was a bad coil swapping wouldve made the miss move and it doesnt. Bad injector?,but then why is the miss gone after a restart???

 

could be the wire harness to the injector or the coil. Misfires across the range of cylinders could also be a fuel trim issue - intake or exhaust air leaks etc. As to choice of plugs - why not just go with OEM Volvo, and make sure they are correctly gapped. Any other symptoms like cold starts, oddly behaving temp gauge to suggest your ECT is wonky? If you have a misfire staying at #2, you could have a valve issue (compression test/leak down to diagnose).

 

The weird thing though is that the miss goes away after a restart. Then comes back only if taken over 2500ish rpm. Tried getting Volvo plugs from the local dealer and they dont stock them.

 

check out Tascaparts.com and other dealer web stores. I like Tasca since they are near by and have the best prices.