I had a very similar problem, I did a post about this awhile back.

https://landroverforums.com/forum/sh...ad.php?t=35967

The coolant temp sensor that talks to the ECU is right ontop of the engine on the front.
It is a $15 part and takes literally 5 min to change.

 

so coolant temp sensor seems to be the big consensus, and Spike, I remember your post, actually it was more of a trivia question if I remember right, and that was what had me thinking that. So if that was my problem what kind of a difference would there be from normal? because it is not really bad, although who knows, that sensor could be failing intermittently!

 

I do not know what the MPG difference would be, mine started to drop off slowly, then all of a sudden one day she was drinking gas.
I had first thought my O2's were just getting tired and I had planned on buying some new ones but before I did my MPG went south quick.
The only way you will know for sure if it is your coolant temp sensor is with a OBDII code reader that also reads live data.
Thats what I did, I plugged in my scanner and watched the engine temp while on my way to work, and then again on my way home and that showed me what the ECU thought the engine temp was.
Obviously your engine temp should not go from -45 to +200 and then back to +50 in seconds.
Thats what mine was doing.
Is that your problem?
I dont know.
Live data is your friend.

 

OK I read the resistance on the sensor with the engine idling at normal operating temp (had just got back from a 4 mile drive) and the ohm reading was fluctuating between 260 ohms and 350 ohms so according to what you guys say this is in spec. now can this sensor start to go bad where the reading goes off the chart like half the time but give a good reading the rest of the time, or is it more like a fuse where it is either open or closed?

 

I have no idea.