So for the last week I have been having an issue where the brake pedal is super hard as if the brake booster is toast but when the car warms up the pedal goes back to normal. It seems to be fine from then on until the car completely cools down again.

Anybody have any ideas? I would think if it was a bad booster the temp of the car wouldn't make a difference.

 

I'd take a look at the check valve in the vacuum line between the engine and brake booster. If it sticks in the closed position, the booster won't see the vacuum, and that makes the pedal hard.

 

The valve is between the engine and the booster? I thought I read that it was between the engine and the battery compartment.

 

The check valve is built into the hose that's closest to the booster assembly. You can see in the diagram here marked 47474:

http://www.courtesyparts.com/350z-pa...5_806_813.html

 

That probably explains alot. I ran a fuel system cleaner through that tube and it probably gummed something up.

 

Don't touch any of that garbage....... fuel injector cleaners blah blah. It's all a bunch of bs products that do more harm than good to your car.

 

At less than $20 for a replacement hose assembly, it's a cheap lesson.

 

This fuel system cleaning is not bs. I have been doing them on my car since 1996 with always good results. Measurable results.

Anyways. I found the valve and it is in the hose by the battery compartment. I sprayed it with some cleaner and it works fine now.