300tdi disco over fueling

Can anyone help?
My current disco's not been running right since I got it (cough, last april). Seems as though its either over fueling or not burning the fuel properly.
It idles too fast (turned it the throttle as far back as it'll go on the pump) smokes a heap on start and then occasionally when driving dumps masses of black smoke on top of another poor road user. It does that more often when on hills and towing.
I have some ideas what could be wrong but thought i'd ask about abit before I go throwing money at it. Any ideas?
The strange thing is that there's no logic to it. Somedays she runs really nice and others she's a bit moody. Reminds me....
Is there an electric choke on a 300tdi or could it be an electrical connection to thermostat/choke?

if air in take isnt restricted by collapsing pipes or leaks on intercooler hoses ,then get injectors tested

Thanks, injectors were my initial thought but thought the problem may be more consistent and regular with injectors.
I cleaned and replaced air filter and no obvious leaks from intercooler.
Will have to leave injector testing till after crimbo now anyway, thanks.
Ave a gud un!

you could try checking your injection timing, and try taking the cover off the pump (4 screws) an see what position the center point mark is possitioned, standard it should be sitting around ten past twelve position. try taking the pipe off from tubo to intercooler,if theres oil, it may be oil seal gone on turbo, good hunting hope it helpsm8. Dave 300 tdi es.