I think i have a vacum leak?? help me please

Hey guys i did the m90 swap on my mustang 98 v6.
It was tuned and its being doing great for the past three weeks, three days a go i started it and it felt weird and suddenly a check engine light came up...
So i drove it and it doesnt feel as powerful as it did before, the throttle used to be super super sensitive and as soon as i got n the gas it d rev up so fast without hesitating.
Now it hesitates before reving for an instant, usually when the car s running my vacum/boost gauge reads -18 to -16 vacum i am not sure, now sometimes it has -13 sometimes has -14 or -12 it depends i dont know why, something is not right, i took it to check the codes and it said that
the engine is running lean.

Could it be a bad MAF??

We cleared the codes and now am waiting for them to come again so i can get more details, i have drove it for 160 miles already after i cleared the code and it hasnt come back yet but i know there s some wrong so i ll keep waiting for it to come again.

There are no oil leaks or any kind of fluids on the engine , everything seems clean.
I am also running a front mount IC setup

What can i do??

Do i have to drive it hard to make sure the code comes back or what?? its being 160 miles.


i am driving it slow trying to reach no boost so i dont mess anything up, we are also thinking of taking it to a friend that has a smoke machine maybe that can help me find the leaks or i dont know!~!

please help me guys, thank you.

Sounds like a vacuum leak to me. You can use brake cleaner to check for a vacuum leak. Just spray it around every joint in your intake system, including vacuum lines, one by one and listen for the engine to rev up. When the engine revs up you have found your leak. If this doesn't help find the leak then the smoke machine will definately find it. Good luck.

Am not familiar with this, so what ur saying i spray it on every connection pretty much and is the engine supposed to rev up by itself when i find the leak??

and thanks any more opinions would be appreciated

notime speaketh the truth. Depending on what you are spraying the engine will either rev up or start to sputter. Its a little more dangerous but I usually use starting fluid.