Hey everyone, so just a bit of the back story. I've had my jaguar for quite some time now (180,000 miles)and I knew it was time for a little maintenance (sparkplugs, oil change etc.) So I replaced my spark plugs and noticed that I had oil leaking in the Wells. So I bought a Victor Reinz valve gasket cover set ( since the actual covers were in good shape already), and a set of intake manifold gaskets and went ahead to replace the gaskets. I then went on the change out the spark plugs (iridium NGK) and ignition coils. Now my oil leak Problem was solved, but I still continue to have cylinder #4 misfire (although it wasn't nearly as obvious as it was before I changed the spark plugs). I know that the gaskets were placed correctly and that I took my time in tightening everything up according to the appropriate torque, what is it that I'm missing ? How can I get rid of this misfire, and how long can this misfire take place before my coils and spark plugs are ruined because of it?

You know for some reason or another I just want to say that when I took the old coils out, there MAY have been very little condensation on the plugs themselves, I'm talking so little that I want sure if that is the case. Now I live in southern California so, in the morning my car has a bunch of condensation on it, but I'm not sure if that condensation can get into the ignition coils????

For more accurate assistance you need to post your S-Type's model year and engine size....

Did you have the code before changing the plugs and coils? If not, a plug or coil may have been bad from stock. It's rare but it happens. Troubleshooting is a piece of cake. Swap the suspect coil to #2 cylinder. Swap the suspect plug with #6 cylinder. Clear the code and see if the fault follows.

If the code doesn't change, please be aware an OBD II misfire code can mean more than just an ignition system malfunction. It means the power output from that cylinder is low compared to the others. It could mean an ignition problem, clogged injector, low compression, etc. Off my soapbox now...

Bear in mind misfires tend to be bad coils

I personally have not had much luck with the aftermarket cam cover and spark plug boss gasket and seals, which tended to leak after a short time causing the coil pack in that particular cylinder to misfire.

Your original post does not specify if the engine fitted is the 3.0 or 4.0. The earlier 3.0 litre required the inlet manifold be removed to allow access to the Bank 1 spark plugs and coils. If you have the 4.0 litre, it is simple to exchange coil packs as has been already suggested to determine if the misfire changes.

I have also seen cars that have a misfire that does not set a DTC, nor trigger the MIL if the misfire is infrequent.