So, the TPS will only work after 20 m.p.h.

What is the PSI when the tires are warmed up? They are obviously going to be higher than 35 PSI.

So how do you know when to add/subtract, ect?

 

The recommended pressure is always measured cold. It already takes into account the expected rise in pressure from heating.

Keep in mind that the TPS sensors are not that accurate anyway. You should use a good quality gauge to measure your pressure when you fill them.

When you start driving, you only have to go a few blocks before the sensors register. Your tires won't heat much at all in that short of a distance.

 

When you measure tire pressure, you are always supposed to go with cold pressure (say less than 1 mile of driving). My guess would be about a 2 to 3 psi increase from cold pressure to working pressure if you're in about 70 - 80 degree weather (at least in my case).

Best bet for your situation is to measure the cold pressure, then measure after driving around for 10 minutes, then again for 20 & 30 minutes. (Use a good quality pressure gauge too).

So in your case make sure you are at 35 psi cold if that's what's required for your particular situation (I've got a 6MT G, so mine are set at 35 psi cold......it differs for other G models so I'm assuming it could differ for the Z's too).