I'm getting cylinder 5 and 6 misfire codes with random misfire code and misfire on startup code I believe. The motor runs smooth on cold start until it warms up for a minute or two then you can hear it change with a misfire out the exhaust. One thing I've noticed is if I take the oil cap off it has a lot of vacuum sucking into the valve cover and can stall the motor if removed quickly. Is this the way the pcv system is designed on these rovers?

 

The 4.4 is very sensitive to vacuum leaks. If cold and I remove the oil cap, it will stall. If warm, it may recover but would run rough. Think hole in a shining straw. Tiny hole can really mess things up. Misfires could be bad coils, you can move them around to see if the codes move with.

 

I was making sure there wasn't a vacuum leak when I noticed the oil cap was under vacuum. None of my other vehicles have vacuum in the valve covers so I want to make sure that's normal on the rover. Sounds like it might be normal. Thanks