TD4 erratic idling

Hi, I am new to this as I have just bought a 2003 Freelander TD4, which is spot on. I have covered 700 miles in it this week and up until I was almost home it was faultless. As I negotiated a junction and came to a stop the idle suddenly became very lumpy and I could feel it through the gearstick, steering wheel and pedals etc. When I rev the engine it sounds like it is missing until the revs build and then once over about 1000RPM the engine runs smooth again. At idle the rev counter shows about 750 - 800 rpm but it feels like it is idling too slowly.
I continued my trip home with the engine running spot on, but when I stopped the idling became lumpy again. To listen to it sounds like a drum beat and the engine is wobbly, which is transferring through the exhaust and making that wobble. I took the fuel rail sensor plug out and it made no difference to the idle. The exhaust isn't smoking at all but it is smelly, quite strong fumes like being next to a lorry exhaust.
I have tried disconnectin g the MAF and it made no difference. I noticed that in the right side of the engine (viewed from the front) there is a plastic "cylinder" the has a small vacuum type hose coming from the front. The cylin der is mounted just above where the clutch pipe is run and as far as I can tell is not connected to anything, it just has about 3" of rubber pipe from the front t hat doesn't connect to anything! I would be very grateful if someone could anyone offer any advice or suggestions?
UPDATE - I have cleaned the EGR Valve which hasn't helped. The cylinder, I have identified as a vacuum reservior so if anyone could let me know what it connects to i'd appreciate it. there is a vacuum pipe with a 3 way connector near the reservior with a long pipe that goes around the rear of the engine to a connection at the rear LH bottom, i guess near the turbo. Any help would be appreciated. Thanks.

Try disconnecting the plug on each injector individually (engine running) to determine if you have a misfire and if so which injector is causing it.
The bad injectors will have no effect on the running and disconnecting the good ones will make it even worse.
Hope this helps.

You sir, are a spot on bloke! I took your advice and sure enough when I took each one off the revs dropped and the car stuttered......until I got to number 3 injector which when unplugged made no difference at all!

I guess all I need to do now is take it out and get a replacement!

Thanks matey, much appreciated. Hope I can return the favour sometime.

Just to let you know - I put some injector cleaner in a full tank of diesel and after running the car for a good 100 miles the idling came back to normal.....i'll see how long it lasts! Many thanks for your advice.