warm/hot start problems

Hi Guys Im new to the forum , have had a look around after being pointed here by google. I have a 2001 TD4 freelander that has what appears to be a common fault of difficulty starting when warmed up. I have been doing some experimenting this morning. I have purchased a new cam sensor as recommended but the fault appears strange. Cold start always fine, 5 minute drive harder to start, 30 minute drive car takes 15-20 seconds to start. So today I drove my car to get it fully warmed up came home and switched off car. tried to start it straight away, which it did perfectly again and again. went inside to get a cup of tea came back, wouldn't start same fault. took out sensor and put it in freezer for 15 minutes to cool it down, refitted car would not start straight away but was better, again once it got going could turn it on and off with no problem . but if I leave it for a minute or 2 problem comes back?? ideas fellas?? I have new sensor to fit but not sure if its the cam sensor.

any help greatly appreciated