You need to find out the motor octane of that fuel from BP. I'm quite sure it is not 98.

Oh, when you raise the boost, you'll hit fuel cut. You need to install a GReddy BCC to avoid this.
http://www.mkiv.com/techarticles/bcc.../bcc_intro.htm
http://www.mkiv.com/techarticles/bcc...GReddy_BCC.htm

Thanks mate.

If my boost gauge is correct, then i am already running around 14 PSI. So if this is true i should have a greddy BCC installed already? I'll have a look.. What happens when the fuel cut kicks in? Maybe this is my problem?

Fuel cut is very distinctive... it feels almost like you drove your car into a wall, and only right at 14.5 psi (never below that). You may be right - 2nd gear may go by too fast to hit the fuel cut boost level.

Try this as a test :
http://www.mkiv.com/techarticles/ffcd/freefcd.htm
Don't use it long-term or the longevity of your turbos can suffer.

Okay, Supra is back on the road ($700 later)... Now that i've paid more attention, the boost gauge hits about 0.7 bar, So i reckon I'm running the stock boost still. It hasn't played up so far either, nice smooth boost apart from 1 time, in 3rd gear, it boosted nicely, then stopped for 1/2 second then kept going even though my foot stayed flat. It seems the 2 week rest in the garage has fixed some of these problems.. weird.

Another question i have is, From cold start the idle is perfect, sitting at about 1k rpm. When i drive a short distance (4km or so), stop the engine and start it about 15 mins later - The rpm at idle is down at around 400 - 500 and jumps up and down. It might go down to 350 or 400 and almost stall, then jump to 500 - 600 then back down again. Any ideas what might be causing this?

Just curious - what was the $700 for?

The idle issue is likely an IAC problem or a vacuum leak. Is the ecu throwing any codes?

$700 for a new wheel bearing and the labour involved. $210 for the bearing, the rest was labour.

Nah the ECU is all clear..

After doing some reading and searching on google for 'boost leak' I reckon that this is exactly what's wrong with my car. When the boost kicks in it just feels weak and sluggish, maybe overboost?

I'm an absolute noob at this stuff, has anybody posted a how-to?

Extra: Just realised i've never looked at the boost gauge when i floor it. It's all over the place! jumps to 0.5 bar, then down to 0.1.. back up...

Does that scream anything?

You need to pressurize your intake system with an air compressor (up to 15psi should be fine) ... all the way from the air filter/maf back...and listen for leaks. You'll have to rig up an adapter from your intake/maf to the air compressor.

It turned out to be fuel cut!

Awesome - glad you got it figured out, and even more glad that your Mkiv Supra TT is behaving exactly as Toyota built it to.

What I'd be a bit critical of is *anyone* trying to raise boost without doing *all* of the BPU mods. The "BPU" spec was written for a reason - so no one would have to worry about stuff like fuel cut when modding their Mkiv Supra TT! Sigh.