2004 XC70 Cylinder 4 misfire comes and goes

[kjhiggins]

A little over a week ago my 2004 XC70 (220,000 miles) started idling rough and stumbling upon acceleration. Initially there was no OBD-II code but it got progressively worse and eventually there was a P0304 code indicating a misfile in cylinder 4. I put new plugs in all cylinders (they hadn't been changed in some time so it needed to be done anyway) and bought a new coil but didn't install it because the new plugs seemed to make it better. By the end of the day, however, it was running just as rough as before the new plugs and the P0304 code reappeared. I decided to use some Techron when I filled the tank on the way home and within 10 seconds of restarting the car after filling up it ran beautifully. It ran great on that tank but then started to run rough again after getting gas and P0304 popped up again. I was away so my wife bought another bottle of Techron and put it in and it again ran great for awhile. Same thing happened again today and then stopped upon addition of yet another bottle of Techron.

What kind of misfire responds to fuel treatment in this way and is always in the same cylinder? The misfire is always in cylinder 4 but I have not changed the coil yet since I returned it when it started running great after the first bottle of Techron. When I get the chance I will swap the coil from 4 with the one for cylinder 3 to see if the misfire moves (if it comes back) but I wanted to get some input on what other possibilities there are for this problem. Any insight would be appreciated. Thanks.

[precopster]

This is all nothing to do with fuel treatment or fuel type.

Once you replace that coil pack it will likely go away.

The only other possibility is that you have the beginnings of a burned valve on cylinder 4 but let's not go there until you replace that coil.

[draser]

Consistent with dirty or leaky injector.

[oragex]

Maybe the fuel pump is going away? That additive could cause better lubrication at the pump

You can also switch the coils from another cylinder to check

[stewed_beef]

I've had the same issue with my 2001 xc, interment misfire on #4.. I tried all the above and noting fixed it but!!! REPLACING THE COIL. After that was done the car has gone 10,000 miles with out a miss fire

[koolhandluke]

Try swapping the coil to a different cylinder and see if the misfire code follows it to that cylinder.

[jgegen]

Same issue with my 2001 v70. Changed the coils and runs perfect now.

[kjhiggins]

Thank you for all the replies. I've been on vacation and away from the car so I could not thoroughly test it until now. I swapped the coil for cylinder 4 to cylinder 3 and now get a misfire code for that cylinder. Ordered a new Bosch coil to replace the bad one.