just_ace
Can of subaru upper cylinder head cleaner.

Ah... Not sure where I should look for that?
Ideas?
 
I'm pretty much a noob and I don't have many tools or utilities that are car-related etc.
 
With that said though, will definitely look into the throttle butterfly being sticky!

Subaru parts service dept, $20

I wouldn't concentrate on that. Sort out your MAF sensor first and I think you'll find that all of your issues will disappear.

Agreed.

But looking at it is free and doesn't take much time.

It's possible your VVT-i isn't working correctly either, although that would probably throw an engine check light I would think.
Without being able to find a super-rare factory SW20 BEAMS airbox, the SARD kit mister2 suggested might be your next best option...

I'll see if I can clean the Throttle and possibly the ISCV as well.
 
I'll also have a look at the MAF and will definitely get the SARD intake in the near future, as I'll need a decent intake anyhow.
Not sure if I can find a spare MAF to quickly test with though, that might be an issue. Don't want to fork out money on a new one and find out that it still runs exactly the same :/
 
EDIT: Reason I want to look into the ISCV is because I found that it might be reason (http://www.6gc.net/forums/index.php?showtopic=90718&st=0). It's also not too hard to service and/or replace by the looks of it.
 
Also worth mentioning, I've had some very occasional issues where my idle isn't always ~850-900 RPM, but rather 1k RPM. It's not a huge difference, but definitely not consistent as it should be.
I've read somewhere that the BEAMS should idle around 750 RPM.

Can you post up some images of what your intake setup looks like? 
 
Do you have the SW20 S shaped black pipe with a pod filter on the end or the shorter Celica piping?
 
Mr2 factory Beams intake:
 

 
Celica factory Beams intake:

 

Here's what the Sard EX kit for the SW20 Beams looks like on the factory piping. If I was you i'd be buying that Sard kit as it comes with the critical part where the MAF bolts too. Then if you don't have the sw20 black S piping get the part number and order it online.
 

 

Yeah, I looked into the SARD intake kit, found a couple places online, this seems to be the best option thus far (inc. shipping to VIC, AU): http://www.rhdjapan.com/sard-sports-ex-plus-top-intake-toyota.html
 
I have the shorter intake unfortunately (which makes sense as far as matters go, as the donor was an ST202) :(
Which means I get even hotter air. I have the elbow from the engine, and then the MAF is there and my intake (Simple Pod Filter) is bolted straight onto that!
 
I've tried my mate's intake, which is meant to be good, it ran through closer to the vent like the S piping, drove it around for 5 minutes after resetting the battery, not much of a difference, just sounded fancier xD
 
Anyhow, here goes a pic...
PS: I am not running that super long plastic pipe that goes from the MAF to the vent. I've removed it since, and I've barely noticed a difference btw.