2000 S40 1.9T: Sometimes, usually after the car has been sitting for a while, it misfires on cylinder 3 (code P0303) for about a minute. If I start it and let it idle it takes about a minute or 2 until it idles fine, then I have no problem for the rest of the drive. If I put it in gear and let it roll (automatic) it rolls for about half a block and then its fine. If I turn it off after it ran fine and restart its fine. Sometimes I can let it sit for hours and it starts fine.

Here is what I have done so far:
Pulled codes: P0303
Checked spark plug, its fine and correctly gapped
switched plugs 2 and 3 just to see if the problem moves
checked the (about 1 year old) coil pack and it looks fine
cleared the codes
Next morning: misfire on cylinder 3 (Code P0303)
replaced the coil with an older but still working OEM coil
cleared the codes
Next morning: misfire on cylinder 3 (Code P0303)

I run only premium gas, whenever I can without ethanol (doesn't always pan out)

I assume its not the coils or plugs. How do I go about testing further? What components are in question and how do I test them?

 

I'd never trust the misfire code to tell me which cylinder. Check all the plugs and coils and wires as a system. When last I had a misfire it was the coils. It did not go away after a minute or so though....

During the misfire does it smell rich or maybe the exhaust glows because it's lean?

Did you check each spark plug's color? Is one different than the rest?

 

I talked to my local Volvo repair shop and the tech said it could be the head gasket slightly leaking coolant into the cylinder. I will depressurize the cooling system when I come home to other and park the car for the night to see what happens. If that fixes it it is the gasket. if not then I guess it it time to switch injector 2 and 3 and see if the problem moves.
Following Hudinis advice I will also look at all spark plugs but since the problem only occurs during the first minute of runtime in the morning I doubt it is an ignition issue.

 

If it's a coolant leak you should see one bright white spark plug (literally steam cleaned). Also, you should get white smoke out the exhaust (steam again). Much thicker than normal warm up condensation. It may smell sickly sweet like coolant. Plus your coolant level should constantly be low.

I'm just trying to get my head around what would cause a misfire only when cold, then go away as the engine warms. That's why I mentioned a rich fuel smell or a lean glowing exhaust. If the coolant temp sensor is bad it may be telling the engine it's either very warm or very cold which causes the ECM to subtract fuel (hot) or add fuel (cold). Once the car goes into closed loop after a minute or two then the fuel trims are adjusted and all is well. The problem with that theory is that the check engine light should be on for the bad sensor. Just a guess.