So long story short I bought a 2003 Land Rover Discovery 2 sight unseen for $500 about 10 months ago. It'd been smoked in, had about 75,000 miles more than I expected and was missing on 4 cylinders and had low oil pressure. I did about everything but pull the motor and discovered the main problem was a broken rocker shaft over the last valve of cylinder 7 and a dropped valve seat on the same cylinder. I repaired all of those problems, did a tune up as well and enjoyed a few months of the smoothest 4.6 I've owned thus far and the entire truck looks great but unfortunately the truck has started to have a strange misfire that i'm having trouble pinpointing. So upon start up the truck typically runs smooth, revs to 1500 then backs down to a smooth 600ish idle, upon driving you seem to feel a small shudder or a skip but not a full on misfire. Upon driving the truck acts odd between 1300-1800 rpms, sometimes when your in this range all it does is a slight judder occasionally that you barely feel all the way up to a full on misfire with flashing SES light (often it wont even throw an SES light). The problem goes away above 2000 rpms and the truck runs fine. Additionally, When you sit at a traffic light in Drive the truck will shudder every couple seconds and it wont do it as bad if you shift to neutral. When it does trigger a light the only codes I get typically are: Cylinder 4 misfire, cylinder 7 misfire, multiple cylinder misfire, and rough road sensor. I'm just looking for any ideas on what would possibly cause this without throwing parts and money at this as I also have a 99k mile 04 D2 that I'm restoring at the moment. At the moment I'm considering throwing a coil and some new plug wires at it ( plug wires were replaced but the 7mm magnacore wires are not the best I'm discovering ) but am open to anybody's ideas. The truck has 245,000 miles so I was thinking possibly bad injectors too? I haven't gotten any o2 sensor codes but I'm figuring I should put those on the list to replace sooner or later. I know this is a lot but its a strange misfire to me with it being there sometimes and sometimes not and then other times being a legit car shaking misfire. Any suggestions are appreciated, thanks! Pic of the truck below.

 

I would change the fuel purge Valve with the Hyundai one
also check or better replace the connector where your o2 sensors plug into

 

Also you can switch coil packs and see if misfire follows. Coil packs are cheap at rock auto. Bosh brand

 

Well with the trouble it is to get to the coilpacks if they're coming out they're getting replaced I guess. I'll look into the purge valve. It's just such a strange misfire though because today it barely did it at all but some days its pretty concerning.

 

My purge valve sometime wouid get stuck open dumping vapours into my intake causing terrible misfires

 

Interesting, did you get a code for your purge valve though?

 

No code for purge valve as it still thinks it works fine but o2 sensor codes and misfires Exhaust will also smell