either your batteries are not pushing enough cranking power with the addition of the stereos, my problem was i had to clean the TB and MAS. afterwards car fired up no problem. but i am running stock stereo and your problem sounds like it is more related to that. my tb and MAS housing were a lil dirty from shipping and the polishing problem.

 

lol same thing is happening to my sedan after i replaced the battery, still havent tried anything to fix it. I havent driven it much though, hopefully ill get to it this weekend.

 

has anyone figured out what causes this? The one thing we have on common is changing the battery. driving me crazy.

 

nope, not the alternator. After sitting all night battery was reading 12.6 with the car off and 14.5 running. Its not that the car doesnt have power but more like it has no idea where the warm idle should catch. When its cold it idle around 800 and works its way down as it warms up but when its warm it runs at 800 for a few moments, then adjust to the lower idle but just bottoms out instead of catching around 650ish. My 350Z has actually started to improve not messing with anything so I am thinking that I will just let them be and see if they fix themselves.

 

Yea those are the first things i checked also and my alternator is good. Same thing happens to mine. On a cold start it'll start perfectly but once ive been driving it and shut it off then turn it back on itll just shut off. Once in a while when i start it the rpms will drop and i can feel the car shutter like it wants to turn off, then the rpms will slowly rise and it'll stay on.

 

With both of my cars the issue has slowly gone away without doing anything. I think it just takes time for the ECU to relearn.