Don't post much but learn a lot from reading posts, thanks to everyone for your wealth of knowledge, I have made nearly all my repairs with the help of this forum!
I bought my 2002 Discovery 2 with 24,000 miles on it about 6 years ago, now has 116,000
I've been dealing with an engine miss and rough idle for about 6 months now, I'm stumped!
I am getting codes
P0154
P0141
P0161
P0304
P0306
Occasionally I get at P0307, P0302 and P0308 but only maybe once or twice in the last 6 months?
The misfires are under load, the rough idle is all the time
Work done
Head Gasket at 80,000ish miles
Recent work
MAF
O2 Sensors (all 4, tried 2 different sets and swapped sides)
Coil Packs
Plug wires
Plugs
Catalytic Converters
Checked for Vacuum leaks, haven't found any
I am currently on my first tank of injector cleaner and the codes aren't coming quite as often?
I'm going to fill tank again tomorrow and try another tank of injector cleaner
I'm stumped?
What else can I check?

 

Nice find on the low mileage Disco.
Do you frequent the same gas station?

 

I have 2 gas stations I use most of the time
I think at this point it might be a wiring problem?
The wiring from the O2 sensor plugs looks good, at least what I can see but I am wondering if the harness for the passenger side front O2 sensor that goes behind the block might be bad
Most of the time I just get a P0154 code, miss is normally P0306, others pop up occasionally though

 

Hmm Misfires on six and no clue why?

Have you ruled out a cracked block?

 

4 and 6 are on the same coil, and are adjacent to each other in the block. I would stand by swapping coils left to right and see if the misfire codes move. If they do you have a coil problem. If they do not, I would then swap 4 and 6 injector with 2 and 8, see if the misfire codes move. If they do not, then I would check the compression on 4 and 6, it is rare but possible you have small hg leak between the cylinders. I would also recommend charting the 02 sensor voltages using the Torque app and posting the graphs here, front ones are the only ones that matter. If they are not cycling correctly and are low then you may have plugged injectors. Also, most of us do not memorize the trouble codes (except for 030X), so it is good practice to post the code and the meaning behind it.

 

I've thought about the coils and plug wires, the first MAF I put on didn't work and one of the first set of 02 sensors was bad (all Bosch or OEM) so it's very possible I have bad coils but I occasionally also get misfires on the drivers side, odd number cylinders as well?
I think if I go to the trouble of removing the intake again I'll just replace everything, coils, wires, injectors and I'll get a good look at the harness for the O2 sensor that goes behind the block
If that doesn't solve the problem it will at least give me a few years before I have to do it again.
I was hoping for something simple to check but I think I've done all the simple things...

 

Also, just refilled tank and starting on my 2nd tank of injector cleaner, first tank was Chevron Techron, now trying Seafoam, hoping it helps but not optomistic

 

The simple things are graphing the 02 sensors. We can determine if the injectors are lean from those. We need you to check both at idle and at highway speeds. Also graph the short term and long term fuel trims. You can throw parts and money at if you like but then it is still a mystery, swapping parts if a solid test of A vs B and helps us rule out parts conclusively. We have had members have bad injectors and bad coils that were new out of the box. Better to swap with known good.

How soon after clearing codes do they come back, immediately or does it take a few drive cycles (3 is typical). Run fine on the highway, miss at idle? What if you clear the codes going down the highway, do they come back

 

How do you graph the O2 sensors? Sounds like it could be helpful
I have a Scan gauge installed on the car, that is how I read the codes, I know you can monitor a lot of things with that, is that what I would use?
I also have scan tool I might be able to do it with?
I'm all for not throwing money at it

 

The android torque app will graph data - you need a elm327 bluetooth dongle to go with and android phone. There are some other scan tools that graph also but too many do the research and list.