Rough Idle, vibration at low RPMs, struggling with speed in 5th gear.

I have a 2RZ 5 speed. It's the first manual I ever owned, so I'm not sure if those issues are normal: When the truck is in idle, it has minor vibrations and sounds like boosted bass. Sits at 750-900 RPMs. When I'm in any gear, and I slow down, the RPMs drop with speed. As soon as the RPM drops below 1500 the truck sounds like there's subwoofers in it, like heavy bass beating. I also noticed that when I'm on the highway in 5th gear, and I go full throttle, the RPMs rises extremely slowly with speed.
For the rough idle, I took apart the throttle body, cleaned it and cleaned the MAF. Checked the plugs, they're just worn but not burnt or anything, the coils are also not burnt or super dirty. I don't think there's a clutch slip either. I wonder if there is a fuel delivery issue, like fuel pump of filter, maybe injectors... perhaps vacuum leak, which I don't know how to check properly.
The truck has 221k miles, so I know a lot needs to be inspected and replaced.

Does anyone have experience with these symptoms? Any more questions or suggestion is welcome, thank you so much.

 

This video does a pretty great job of breaking down the components of the throttle body for a 2RZ and how to make adjustments. At least helpful for further diagnosis. My initial thought was that your IAC valve is clogged up but that’s only because you didn’t mention touching it. I’d play around with the throttle body, make sure everything is cleaned out well, adjusted appropriately and also test the electronic components (IAC, TPS).

https://youtu.be/GVWCCjZBfGM?si=P5Psui6FfWK-qxPt

 

It's missing on a cylinder or two, that pretty much explains all your symptoms and lack of power.

Now you need to find out if it's due to mechanical issues or electrical issues.

 

Thanks man, yeah I came across this video earlier actually and the TPS is the only thing I have not messed with. I'm gonna test it with a multimeter and clean it ...

 

Thank you for the insight, could you elaborate on what kind of elec and mech issues it could be? like electric issues as in sensors, and mechanical as in plugs?

 

Plugs, [cheapest and easiest, always start there] coils, fuel injector/s, all the way to a cracked head or burnt valves.

 

Roger that

 

Thanks for vid ztwatson
After my TB/IAC cleaning I was wondering about same plunger and if needed to be adjusted

 

Well boys, I changed the plugs and now I have a check engine light lol I put everything back how it was, I’m very confused

 

What code are you getting? Could be as simple as a connector left out

 

P0110

 

I'd check your MAF. Did you pull it and maybe get some debris on it when you did the plugs?

 

I didn’t take the MAF out only unplugged it, only took the snorkel and filter out so I could get to the plugs… don’t remember disconnecting anything else tho