I recently acquired a 2003 land rover discovery with 100k miles which has been running fine for the past two weeks until a few days ago it threw some codes. Let me also mention I wanted to give the rover a tune up and replaced the plugs wires and coil packs. The first codes were P0130 and p0150 which are 02 sensor codes. So I cleared the codes and they returned the next day except with a few more codes this time. I now have p0300 and p0307 which from what I found are misfires cylinder 7 and multiple cylinders. Every few start up it will have a rough idle. Now I am worried I have a head gasket leak but what else could this be? Any troubleshooting besides a compression test I can do? Would new o2 sensors help with rough idle and misfire codes?

 

Not sure why you are asking, the codes say you need 02's so I would do them first.
When was your truck last tuned along with new 8 mm silicone wires, what octane gas are you burning and have you been having to add coolant lately?

 

Well the question remains to what wires you used? And did you put dielectric grease in the boot ends of the wires? Are you absolutely positive that you have the wires seated properly on both ends and then the electrical connector that plugs in to the coils are those plugged in all the way?
Also you could check your connections at the o2 sensors for oil and grease and dirt build up they like to collect there and set off codes.
Now for your assumption of head gaskets failure is odd unless you are loosing coolant or have milky oil? If you have a head gasket water jacket leak on cylinders #7 & #8 it tends to leak down the back side of the engine on to the oxygen sensor connectors and again fill them with gunk and set off codes.

Investigate all the possibilities i have mentioned and please do get back with us! Look foward to hearing from you!

 

Unfortunately I do have a good amount of oil and what seems to be an oil leak coming from the back side of the engine. The driver side o2 is covered with more oil and gunk than the passenger side and from what I have learned the cylinder 7 is on that side, right? I can hear swooshing of water/coolant when driving but I may have created an air bubble in the cooling system when I had to disconnect one of the coolant hoses to take the intake manifold off replacing the wires/plugs/coils. I just now checked the plugs and they look fine and also added some coolant and ran the truck until warm and bled the air out using the bleeder valve on the t-connector of the cooling system. I only use premium gas btw. I used auto lite double platinum plugs and very small amount of plug lube on the wire boots. I checked and double checked the coil and plug connections and they are all tight and connected accordingly. Before I go spending more money on this truck, shoul I get some new 02 sensors? Can these cause multiple cylinder misfires? Anyone know a good rover doctor in va close to fredvegas?

 

Passenger side is number 7 buddy. Now you need to unplug the o2 sensor and dry it out and put dielectric grease in after it dries out. And then bleed the cooling system.