I think you need to get the inlet manifold off and give it a thorough clean. It's most likely coked up with carbon to the point where the engine is seriously struggling for air. Forget in situ cleaning products. There's nothing you can put in the air intake that will clean it, and on which the engine won't run away. Dismantle and manual cleaning is the only way to do this. On the bright side when it's done you should have an engine that runs better than it has for a long time.

Diesel engines don't have a throttle like petrol engines do. Instead engine speed is controlled by fuel metering. The air intake is open all the time. Most modern diesels do have a butterfly valve in the air intake but it's not a throttle and does not control engine speed. It's to ensure the engine stops quickly when switched off by closing the valve and blocking the air intake.

Hi if been reading on other forums that the swirlflaps are a problem on the BMW engines what else could it be and if I do swirlflaps where is best place to get the blanks from thanks

You haven't really been listening. The intake manifold is probably bunged up with carbon deposits and restricting inlet air flow. There's probably nothing wrong with the swirl flaps. There isn't much that can be wrong with them. They just need a good thorough clean so they can open and close freely. There isn't any other way you're going to do this. It's a dirty job but it needs doing.

Yh will do as its my mates car we will have to have a look ?

Once again, air flow. Loss of air flow = reduced MAF signal.