Just an opinion from a guy with a motor way more tired than yours. The lower the vacuum the higher the output from the MAP. The highest vacuum is at idle, when you have the highest restriction and again when you hit a sweet spot in the RPM band with a constant throttle and load.
The only thing I normally use a vacuum guage for is testing valve seal, the needle should be steady and have no pulsing.
The narrowest part of the TB after the IAC is likely to be the highest true vacuum.
Vacuum is relative and constantly changing with throttle plate position, RPM (cam) motor trim and where you measure it on the intake.
Constant low (or high) idle on a hot and cold motor is likely the TPS, either the ground or the signal somewhere in the wiring between the TPS and the ECU. Try changing the TPS adjustment incrementally and see if it changes your idle (after testing the ground). I found the best spot for mine is somewhere between where the book says the tranny half of the TPS should be set and the stick shift adjustment of 0.08 volts on the ECU half of the TPS. My butt dyno says I get decent shifts and a decent idle.
Low idle on a hot motor, try unplugging the O2 sensor and see what happens. One of the things the ECU is going to try and do is supply enough oxygen to the CAT for a good catalytic reaction, sometimes the programming compromises the fuel/air mix and it screws with the idle.
Again just an opinion, the programming in the ECU isn't perfect, It isn't going to deal effectively with any and all inputs and circumstances. They did a pretty good job programming it, but not perfect. I'm fairly anal about most things, but have learned to compromise some with my Renix. I never have gotten a 600 RPM idle, it idles at 500, thumps like a metronome and never misses a beat, I'm happy. My biggest issue was a ground splice for the TPS between the bend at the firewall and the connector, the splice is inside the harness sheath. I had a (ground) splice that was never crimped and the wires were just laying in there, ohm test good. As soon as I cleaned and soldered that splice my idle stabilized at 500 and my 2000 RPM hot starts disappeared.
I used a drill bit to clean out the MAP orifice on the TB and regularly check out the TB to MAP vacuum line. My method is to plug one end of the line with my finger, suck until I get a good vacuum and vacuum glue the end of the line to my tongue, If the vacuum releases you have an issue.
