Replacing the vacuum lines is probably one of the most important
reliability upgrades one can do to a 3rd Gen. RX-7. The stock rubber lines
age prematurely in the hot confines of the rotary engine bay. They become
rock hard and brittle, causing them to crack and come loose from their
attachment points. The most common cause of engine problems and misbehaving
turbo operation is a loose vacuum line somewhere. I won't go into the specific
"how too" as there are much better descriptions elsewhere but I will submit
some words of advice based on my experiences.
Replacing the vacuum lines requires removal of the plenum - an intimidating task but not too difficult.
All electrical connectors are unique so they only fit one way - it's impossible to mix them up. There is, however, one blue connector that is for use on CA equipped vehicles only. Don't panic if you can't find the other end of the plug, your car simply may never have had one. Check the emissions sticker on the underside of the hood if you don't know whether you car is CA equipped.
Then there are the vacuum lines - almost 60 topside and about a dozen down below and in other places. My current count is 72. I used various sizes to replace the stock ones with: 3.5mm, 6mm, and some 8mm.
I attached them using zip ties, small metal spring clamps (for the turbo actuator lines - they melt zip ties!) and weather-strip adhesive.... being very careful not to block the attachment nipple with the adhesive!
Do each line ONE AT A TIME.
Buy a set of long handled, long tipped needle nosed pliers - they are invaluable when doing this job.
Be very careful when removing the old lines from the solenoids. The solenoid nipples are plastic and will break off very easily. If there is any doubt that it won't come off - slit the hose lengthwise then work it off. Break a solenoid and its $50 from a dealer.
Make sure that there is no possibility that a line will kink -there are two lines that were particularly difficult to get right. A kinked line is as good as a blocked or unconnected line.
There is one metal nipple (both ends) that is not connected to anything. It is for use on automatic transmission vehicles only.
I did NOT remove the rack to do this job. HOWEVER, there were two lines that I could not do. I glued and tied the accessible ends and keep my fingers crossed. It's been two years since I've done my lines and so far no problem.
Replace your spark plug wires while you have the plenum off. It is A LOT easier!
Make sure you cover the lower intake manifold ports with tape. Drop a nut down there and your are in deep trouble!
Below are some pics of us (me included) replacing the vacuum lines on Paul Ober's car - an identical setup to mine. Click on them to see full size images.