Checked the EGR vac hoses and it's not that, checked injector o-rings it's not that

Sounds like a really loud boost leak, the car idles rough, goes from 1800ish down to 1000, back up again after awhile. Service engine light is on as well.

anyone ever had a problem similar to this?

 

I had a similar problem, no CEL though. It turned out to be what looks like a brass circular cap that's pressed into the back of the throttle body. When I took out mine it had what I believe is a stepper motor, there's 2 small metallic parts that are a PITA to align correctly while putting back in. Put a little bit of Red RTV and pressed it back in. No boost leaks since.

 

What's the code?

 

Was reading through some threads about that, I hear that cap is only on 03/04's

P0171
system too lean, cylinders 1-4

says probable cause

Ignition system faulty
fuel system faulty - Injectors or pressure
Vacuum leak
Engine Mechanical Condition

for some background, the fic 1250's were just put in and the car is tuned on e85

Could my intake manifold gasket be causing a leak?

 

Yes