I thought all P38 2.5 DSE'S lost power going up hill and also were sluggish when cold. Mines been like that for the last 160,000kms and that's why my mates call it the "green slug". If your RR ran ok before you addressed the fuel pump leak and now you have a problem, surely it can't be down to the MAF, MAP, or IAT.

It does feel better today. It tended to lose a little speed up the hill this morning. But it’s hard to say if it was really better pre leak fix. I do know it’s not a super sports car. Or a 6th generation jet fighter. Or a space rocket. Etc.

Now I’m determined to fix what I can. I suspect the IAT haven’t worked since I purchased the car. If it’s fixable it ought to run a little better with it than not if I’m not mistaken.

kretslopp said:

It does feel better today. It tended to lose a little speed up the hill this morning. But it’s hard to say if it was really better pre leak fix. I do know it’s not a super sports car. Or a 6th generation jet fighter. Or a space rocket. Etc.

Now I’m determined to fix what I can. I suspect the IAT haven’t worked since I purchased the car. If it’s fixable it ought to run a little better with it than not if I’m not mistaken.

Click to expand...

The IAT sensor is used along with fuel temp sensor and engine temp sensor to fine adjust injected fuel quantity. The MAF sensor other than the IAT sensor it has in it, has nothing to do with fuelling. Airflow is not a consideration only air temp. No diesel engine gives it's full power potential from cold. The ECU restricts fuel, so controls power available until a working temp is reached to reduce emissions. With no IAT data available the ECU will use a preset air temp to fine adjust fuel quantity. If it uses the -38.88 figure preset in the ECU on MAF equipped M51s, that means the fuel quantity adjustment will give minimum fuel for any throttle demand for emission purposes. Because it thinks the air is thick and dense. The fuelling map on the M51 Range rover engine is set lean with different torque curves than those fitted to saloon cars with the same engine. Chipping can increase power and torque considerably. But does have some drawbacks.