All the Help I can get please
 

1. Got my car back from nissan had a little overhaul done and for the 1st 3-4 days it rode beautifully. 2. I originally posted assuming I had a bad detonation sensor because after the 3-4 days I was locked in safety boost. 3. Grounded the green wire and also wired in a resistor and no more safety boost but the car is still not performing right. Its not as responsive and the idle is a little rough. 4. Noticed that the temp gauge no matter if the car sits for days or minutes always jumps to the middle of the gauge no matter what?
Why is my car doing this, why is it not responsive like when i first got it back?
All help is greatly appreciated

is it throwing any other codes?

nope. no other codes. I just drove it again and the boost doesn't reach 14-15 anymore it looked like it was more around 12-13

Also when i pull the throttle open slightly and listen toward the rear of the engine i can hear an air "pssst" noise coming from the back top area of the engine. Thank you guys for the help

Sounds to me like an air leak. You need to find that and seal it... that would affect performance and peak boost.

As for the coolant sensor... it's either a bad gauge sensor or the wire is crossed with another. Disconnect the sensors on the coolant pipe (I don't remember which one is for the gauge) and see if the gauge drops. If it doesn't drop, it's a wiring problem.