That means it's possibly NOT the suction control valve.
Things to check now:
* Air filter. Remove it and inspect it. If it's discoloured, try another one.
* MAFS. It's the sensor just outside the airbox in the rear of the hose. Remove it, spray some electrical contact cleaner into it, reinstall it.
* Stuck EGR valve. Blocking the EGR will not harm the engine and might relieve the symptoms. Remove the gasket on the inlet manifold side, make a copy of it in stainless steel without the big hold in the middle and put the copy in its place.
* Fuel line leaks. Try squeezing the primer bulb. It shouldn't take more than 5-6 squeezes before it's quite firm. If not, there's a possible leak on the suction side of the pump. Make sure hose clamps are on firmly but not overtight (they can pinch the hose causing the leak!). If the fuel filter has been replaced recently, immediately suspect the seal, it's a common cause.
They're the easy and cheap ones. Then it's on to the fuel filter.
* Replace the fuel filter
* Remove and test the glow plugs. Replace as necessary
* Check the output of the fuel rail pressure sensor. If this is reading too high, the ECU will reduce the fuel rail pressure and that could cause the engine to stall.
There may be a couple more things to look at, but that's a start.