Can't locate ANY vacuum lines?!

[recycleoldgrowth]

I can not for the life of me find one single vacuum line on my 2004 chevy 2500 8.1L, also has no EGR valve. I have an Idle bounce and am trying to figure out what the problem is. Took the fuel pressure at the rail. At KOEO was 55psi, KO pressure holds. At idle it reads able 63psi and will rise some with some throttle. All looks normal to me, anyone think differently?

Then took a can of break cleaner to the intake manifold gasket and parts of the TB, nothing. This is why I ask able the vacuum lines, shouldn't there be some or because it uses MAS, MAP, and other sensors to do its calculations it doesn't need vacuum lines?

Truck runs fine, no codes, just hate not being able to figure it out!!

Regards

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[BlackBearPerf]

That's a common annoyance of the 8.1L, no vacuum source to tap into!

Have you cleaned the throttle body itself, specifically behind the blade? We would suggest doing that as well as a thorough MAF cleaning as those are both common issues to develop on the 8.1L.

Fuel pressure looks like it might be a bit higher than spec as well, but that shouldn't cause those issues you are experiencing.

 

[recycleoldgrowth]

That's a common annoyance of the 8.1L, no vacuum source to tap into!

Have you cleaned the throttle body itself, specifically behind the blade? We would suggest doing that as well as a thorough MAF cleaning as those are both common issues to develop on the 8.1L.

Fuel pressure looks like it might be a bit higher than spec as well, but that shouldn't cause those issues you are experiencing.

Yes very annoying for sure. I did clean the TB, tho I didn't remove it, just pushed open the throttle plate and cleaned behind it. I know I took a chance doing it that way but it seems to be fine. Also cleaned the MAF, neither helped.

Tested all my grounds, they all Ohm out. The STFT AND LTFT are +/-5% and the O2 sensors voltage look within spec. Low voltage .02 to .850 pre cat, post cat holds at .645.

Anything else I can look at? I'm wondering if I replaced the throttle body assembly it may fix it?

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