[T77911S]

one is a vent, the other is a vacuum enrichment.

the DV holds the RPM's up then drops them down slowly. more so than just closing the throttle. if the RPM's dont hold then drop some what slowly, this IS the problem.

now, the RPMs can drop quickly and the engine should keep running. so you have more than one problem.

CCP is based on outside air temp.
remove the power to the WUR and check this with the engine off. you will get one reading.
start the engine and if you have the TTV, in about 20 seconds, you should get another reading. should be around .8 bar higher.

connect power to the WUR. after several minutes you will get the WCP reading. should be around 3.6bar.
if you remove the (?)top vacuum line, you will get about a .8 bar lower reading. so 2.8bar.

but, if you are adjusting the big idle screw and not getting much of a change ,i would really start looking for air leaks.