Yes, but GENTLY!

That thing is a 25 year old piece of a 35 year old plastic formulation - it's FRAGILE!

 

Check the blue/black check valve coming off the brake booster. If doesn't hold vacuum in one direction-it's shot and could be the root of the problem. (Thanks Sean R.!)

I replaced it with $5 NAPA part this weekend and that fixed quite a bit of vacuum issues! My Idle dropped a bit; my AC was cold; my shifts were a little smoother from 3-4 (still need to check/adjust modulator pressure at Tranny).

Now don't get the $5 part; get the $15-20 part from 928 International/928sRUs/928 Specialists. The one from NAPA worked until it didn't! POS part.

New part already on order.

 

I missed this comment about the heater control valve when it was first posted, just want to correct for later readers...
"according to the post sited above the valve is unidirectional.. not true..
mine is a straight through valve, does not matter which way it goes in..."

Wrong. The valve has a sliding door that closes coolant flow. If installed properly, flow pressure pushes the door more firmly onto the seal. If installed backward, flow pressure pushes the door off of the seal and allows coolant flow even when the valve is closed.

 

i have since this post found the same information...