I've been trying to diagnose a perpetually slippy transmission in my 81 300td. after adjusting the nut on the VCV, the pressure at idle running to the modulator is 12" but goes UP to 15 when under full throttle. I took the linkage off the valve and when the engine RPMs stay at idle the vacuum goes down to zero as it should when I actuate the lever. Is this at all normal? It seems like quite a number of things in the vacuum system have been changed by previous owners, for instance, I can't find anything like a measured orifice as mentioned here in a variety of places.
Hmmmm... Possibly related: the modulator definitely has a leak and there is a leak at the shut off switch in the ignition but this VCV problem is there without either of those connected.
Any thoughts?
thanks!