Vacuum leak? Help and tips need it to pin point the issue.

All right, this is my first time posting here. I posted on a YouTube video  and I was sent here,  anyways, I've been working on a 2005 scion XB with the 1NZ-FE engine 1.5 liter,   I think it has a vacuum leak thay i cannot find,  these are the symptoms,  the car misfires on cylinder 3 and 4 , and sometimes in 2,  only when you snap the throttle really fast. It also misfires when you press the brake pedal repeatedly,   at first I thought it was a faulty brake booster. Because if I clamp the hose that goes from the intake manifold to the brake booster the misfires disappear  when snapping the throttle or gas pedal,  i replaced the brake booster with and new one and I still have this same issue.  I put a smoke machine in the system and I dont see any leaks. I also use the water bottle trick and brake clean to find vacuum leaks and nothing.  Any tips or advice will be appreciated to diagnose this car properly,    on scan data I have short trim of about 0 % to 2%  and in long fuel trim is have negative 18% if that helps.
Maybe my issue isn't a vacuum  leak.
I'm lost as of today.   It has also new sparkplugs.  I cleaned the throttle body and replaced a coolant hose that goes from the idle control valve ,  because it had a small rip,  I replaced the throttle body gasket and intake manifold gasket. Even tho they look fine.  I haven't started  the car yet. But I have a feeling that I will be having the same issue. Forgot to mention the car drives totally fine when driving normally , it doesn't have any codes, but if I start snapping on the throttle or brake pedal , I will totally get a  random misfires codes on cylinder 4 and 3 

 

Welcome to the forum!
Hopefully you can get this sorted out.
Based on your fuel trim values, I don't believe you have a vacuum leak. Typically a vacuum leak on a mass air flow sensor equipped engine will result in high positive fuel trim values. -18% long-term fuel trim at idle is the opposite reaction.
How are you identifying the misfiring cylinders? Going by codes, live data, cylinder drop testing?
Are you feeling misfiring or experiencing a lack power that lead you to check?
I ask because you said there are misfires while snapping the throttle, but didn't mention anything about overall performance.
Codes and scan data aren't always fool proof and can be misleading at times if you aren't used to using the data. For example, if you are seeing one (or two) cylinders with very high misfire counts, and other cylinders with just a few, it's a safe bet that most of the time that the cylinders with very low numbers aren't actually misfiring at all and that fixing the problem on the cylinder(s) with obvious misfires will correct the issue.
If 3 and 4 both have significant misfiring under load, (any time two cylinders next to each other misfire), I start thinking about a cylinder sealing issue. Head gasket, cracked head, cracked block, that kind of failure. You may want to verify mechanical integrity before going much farther. Relative compression with a scope, traditional compression testing with a gauge, and/or leak down testing would be high on my list of tests.
New plugs is never a bad idea from a maintenance stand point, but I don't see you mentioning that you have verified spark from the coils during the misfire. I like to use an adjustable spark tester for this because it lets you really stress test the coils and see if they are breaking down under load without actually having to go out and beat on the car.
Let us know how it runs when you get it started again.

Hello, thank you for replying. The identity the misfires thru live data, on my scanner. I can definitely feel them , if I keep snapping the throttle, [gas pedal] or brake pedal. At idle only. I will get the misfires. If I keep snapping either pedal for like 1 minute I will get misfires codes to set on my scanner and check engine light. P0300 P0304, the misfires are only at idle when snapping either pedal. The car drive normal under load. Highway or crusing, no misfires then. I discovered this when I was bleeding the brakes with the engine running. If I clear the codes and just drive normal it will never set a misfire code. And passes emissions. Under high load the long fuel trim goes to about -5% , I cleaned the throttle body . But I haven't put the car back together since we are in a middle of a storm right now. I did a compression test on this car about 7 months ago and it had good compression on all cylinders.

I agree with Noah about the misfire counts. It's not unusual for a misfire monitor to flag miss counts on cylinders that aren't necessarily misfiring. Since the ECM set P0304, I'd put money on #4 being the suspect cylinder.

Yours reminds me of a Prius I fought a few years ago. Persistent miss codes, would only count during a throttle snap in the bay. Fine just fine otherwise. Came down to a fuel injector with a poor spray pattern. Moved the injector to another cylinder to prove it.

I'd consider doing some musical chairs with the injectors. Move #4 to #2, #3 to #1. That gets the suspect injectors opposite positions in the firing order, giving the misfire monitor a better chance of catching a change.

I finally found the root cause yesterday, I want to thank Noah for suggesting a cylinder compression test, I found low compression on cylinder 4!! I assumed the compression was right because i did perform a compression test 6 months ago on this car, lesson learned, never assume just test and gather data. Cylinder 1 ,2 and 3 , have a good compression of 180 psi, while Cylinder 4 has a compression of 156 psi! Thats the minimum allowed for this engine. But the difference between the rest of the cylinders is too much. I put a spoon of oil at the faulty cylinder and compression jumped to 180psi, which confirms piston rings are the culprit. Thank you guys for your replies and help. I appreciated it. 🙏

Here is a couple pictures of cylinder #4 compression test before and after adding a spoon of oil in the cylinder. 

It could be cylinder wash from lack of combustion. I would take Tyler's advice and swap that injector for another one before condemning the engine just yet.
Also, is it just be or is there one odd ball blue injector in cylinder 2 and green injectors in 1, 3 & 4?

I will try swapping the injectors to see if the issue moves to another cylinder. These injectors were replaced by the previous mechanic , they are not brand new. They are "rebuilded oem" they were tested supposedly. But I will definitely will swap injectors.

FSierra86, did you happen to get around to moving injectors? Not nagging, just genuinely curious, especially after your compression results.