My Rangie is a late 2000 model 2.5 Diesel DSE and here’s my scenario. I start from cold after preheating and she runs, accelerates and behaves just fine. After (and only after)she is hot I switch off and the revs go and stay at 500 rpm. I put the throttle to the boards and count to about 6 before it responds and revs up. Then when I drive I have to left foot brake and keep the revs up to get in and out of traffic !! I had a diagnostic put on and the only fault that showed was ‘fuel temperature sensor’. I have researched this and it seems that this sensor is inside the fuel injection pump and inaccessible – is this the case??? It seems that for the sake of one of these blasted sensors my otherwise good car is rendered useless. BTW I cleaned the MAF sensor with the proper stuff and changed the vacuum pipes between the manifold and hot start/ fuel filter as these were split and delaminated. My question is what is involved with righting this problem … any help would be greatly appreciated.

I should have put 'when I switch off and then re-start the revs only go up to 500' ....

Make sure the fittings are not blocked on the manifold and the MAP sensor on the filter housing. Check your in tank pump works, check/change the fuel filter.
I believe the sensor in the FIP can be changed.