Simple question that I can't seem to find any info on (used the search tool, I promise!).

I'm pretty new to cars, but my friend seems convinced that my lean fuel mixture is being caused by a vacuum leak.

When I pump the brakes at idle, my fuel trim maxes out and spits out a lean fuel code to my obd2 gauge.

 

use google, rather than the search tool. Lots of methods of finding a vacuum leak.

What is your MAF g/s and what is your short term fuel trim while at idle?

 

What he said, and...

I suggest disconnecting the vacuum hose from the brake booster and plugging it with something that will not get sucked in. You did not add a year, so I would not suggest bending it to seal it. it might crack. Then do your brake pump. It will be harder, but it should not impact the engine at all. If the engine runs fine, and then dies when you hook the brake booster back up, issue is the brake booster. It is leaking when you apply the brakes.

Next step is what RIWWP said, read. I do not know anything beyond that..

 

Which lean fuel code?

From the front O2 or read O2

Post CEL