I need some help, I own a 02 Volvo s60 AWD, with 98,000 miles. The other morning I turned my car on and after allowing the car to warm up it started to idle rough, and the check engine light lit up. I took it for a ride down the street and it had little power. I hooked it up to an OBDII reader and came up with the reading of P0304. I looked this trouble code up and read that it meant #4 cylinder was not working. I replaced all the spark plugs, and in the process I inspected each one of them. All had a light coating of carbon, except for cylinder one, which was still slightly wet with fuel. This made no sense to me, becuase cylinder #4 looked like it was burning fuel. Anyway, I changed the coil on number #4 and #1, and reset the trouble code. I started the car and let warm up for about 10 minutes with no signs of hesitation, so I took the car for another ride. First couple of miles the car ran awesome. Then the check engine light started flashing, and the car started acting up again.

Has anybody here had the same problem? If yes what do I do?

 

How old are the coils?
If original I would replace them.

 

I'm curious as to what the 'new' code was?? Did it change to 0301, or was it 0304 again? It still seems like an ignition/coil problem and the CEL code might still be helpful in isolating the problem. Did the new plugs get gapped correctly on installation?

 

Igntition coil on cylinder #1 and #4 have been replaced with new coils. but I will try replacing them all to see if that would solve the problem. I gapped the plugs at .030.

 

Replaced all cylinders with new ignition coil packs, with positive results! Got the car working again. Thanks for your help Guys!