Without major engine work, what else can I do to improve performance in a stage 3 A4 1.8 (DBW)? I notice performance degrades significantly in warm weather. Will an aftermarket intercooler make a big difference here? I'm sure there is a difference, but throttle response is very sluggish when it's 70 degrees outside and right now that's my biggest issue.

Beyond that, is it possible to get the car up to stage 3 + race fuel performance - on 93 octane gas? Can I get there without having to rebuild the engine? If so, what must I do?

In no particular order.

1. Exhaust if you don't already have one.
2. Test pipe can make a few HP as well.
3. An aftermarket boost controller can decrease spool-up time, and maybe bump the boost up a tad.
4. Lightweight flywheel
5. Water Injection
6. FMIC

I ran the 100 program for the past five months on 93 octane gas while temps were low enough. If I wanted to go any later I'd need water injection or a bit of toluene.

Got some of that at my local Sherman Williams a few years ago. Ran it at Watkins Glen for 2 days in 90* temps with the APR v3.1 program. No problems but for a little black soot on my rear bumper.

a nice mbc is the only way to go

My e-bay special was $15, and it worked great once it's set.

Problem is, it's a PITA to set. make a run, do an adjustment, make a run, do an adjustment, make a run, ooops, too much, back it off, arrgh!

I'm going to an EBC, not only because it's cockpit adjustable, but also because I can wire in a switch, and have two different boost settings. I'm thinking one boost setting for normal driving, and another for when the water injection is installed again.

A EBC will keep that wastegate closed all the way to you reach boost. A MBC will gradually open...

And like the other say, possiblities to adjust from cockpit, and have two boost settings is sweet :)

A very nice mod I would say.

I think there's also a way to have an external switch hookup as well, I'll play around with it once it gets here.

That would also mean the unburned fuel was causing you to lose power.