range rover classic 3.9 EFI runs poor and heats up very fast with code 14

I've recently noticed my range rover classic 3.9 efi warms up really fast, at idle in about 2/3 minutes the car is at running temp. the car also sometimes sputters and dies, even when driving. the diagnostics display gives code 14. where should i start? i know code 14 has to do with coolant sensor, the level is fine and replaced the thermostat. where should go from here? also when i hit the gas it drops in rpm and then rises, could this be related?

Can you get an engine temp reading?
Sometimes an ecu engine temp sensor can go and it'll run rich as it can't see the real engine temps
It may have two temp sensors, 1 engine ecu and 1 gauge sensor.

Mark Piercy said:

Can you get an engine temp reading?
Sometimes an ecu engine temp sensor can go and it'll run rich as it can't see the real engine temps
It may have two temp sensors, 1 engine ecu and 1 gauge sensor.

Click to expand...

My 3.5efi doesn't have the facility for code reading, but I changed what I assume is the ECU temp sensor last year & for the first time in 15 years ownership the exhaust tail-pipes are now grey after a run , rather than black

The sensor was in a Lucas branded box .. made in China, but at least it seems to be working properly.

Ain't talking codes dude, are there two sensors on this engine or one?
Old school trick of removing them and checking the resistance while heating them buggers up