Land Rover Repair: Misfire on cylinder #5- 2003 Land Rover Discovery, land rover discovery, k n air filter

Question
Hi,

I have a 2003 LR Discovery I purchased used from a LR dealership almost 5 years ago.  At that time, it had 32000 miles and was given a tune-up by the dealership.  It now has 49000 miles.

Recently the check engine light came on and the resulting error code was 0305- misfire in cylinder #5.

Before this, I had replaced the factory air filter with a K&N air filter.  I verified it was the right part number for the LR.  After replacing the air filter, there was a barely-noticeable sputter when idling but the truck ran strong and I did not experience it again so I thought nothing of it.

Then my fiancee took the truck on a round-trip from Chicago to upstate New York and we have also taken it on short trips around town with no problems.

In total, it's been about a month and about 2000 miles between the filter change and the error code.  Can they be related?  If so, why would it only affect cylinder #5?  Could I have knocked something sorta loose when installing the filter that took a month to loosen up fully?

I would greatly appreciate your help.  The New York trip and other expenses have sucked us dry so I would like to fix this myself if possible.

Answer
With that code, I would start by examining the #5 plug and plug wire.  Is there visible corrosion on the wire?  If so, I would replace all the wires, the plugs (use only oem plugs) and the coil packs.  If no corrosion is seen, I'd change that one wire and the #5 plug.  See what happens.