From a previous vehicle (petrol) the EGR valve works by balancing manifold vacuum against a spring so that at idle less exhaust is recirculated.
With no throttle as such on a diesel, manifold vacuum doesn't change in the same ways so not sure how the EGR is controlled
The other noticable condition with the EGR valve sticking open is that you get a very erratic idle. If you do have one fitted and can get to it, I was able to tap the top of the valve body with the handle of a hammer which caused the valve to shut again.You can then use something likr "copperslip^ to lubricate the moving stem
I seem to remember being told that when diesel give black smoke they are being overfueled and the "fuel rack" (injector pump) needs adjusting
With no throttle as such on a diesel, manifold vacuum doesn't change in the same ways so not sure how the EGR is controlled
The other noticable condition with the EGR valve sticking open is that you get a very erratic idle. If you do have one fitted and can get to it, I was able to tap the top of the valve body with the handle of a hammer which caused the valve to shut again.You can then use something likr "copperslip^ to lubricate the moving stem
I seem to remember being told that when diesel give black smoke they are being overfueled and the "fuel rack" (injector pump) needs adjusting