Get a custom chip. It should run you around $300 - $900. If you weren't willing to spend $1K on a custom chip, or spend 200+ hrs learning the Tweecer, then you shouldn't have gone to a big engine with EFI. Sorry, someone should have been
honest with you about those points.
Do you want to take that time and spend the money to learn the Stang EEC? If so, that's great! Or, do you want to spend your
time on other mods and other things? Most people choose the latter.
If someone told you that you didn't need a custom chip with your setup, then they are full of it! If you have a custom chip, get the problem fixed.
The Tweecer and EEC is *not* something you learn over night. Also, very few really take the time and effort to understand the EEC well enough to tune well with a tweecer. Unless you're willing to put in ~100-200 hours of time learning and understanding the Tweecer and the Ford EEC-IV, don't bother. IMHO, it's *not* worth it for most people.
FYI: My TPS FAQ:
http://www.veryuseful.com/mustang/tech/engine/Mustang-TPS-FAQ.html
Consider this, if you don't want to take the
time to read and
understand my TPS FAQ, don't even think about wasting your money getting a Tweecer. You'll do more harm than good. I'm NOT saying that you "couldn't" learn how to use the Tweecer, I'm saying that "most" people do
NOT have the time or
want to spend the time to learn on how to properly use a Tweecer.
If you are interested in learning the EEC, that's great!
Here's a place to start:
A Quick Overview of the Inner Workings of the EEC (Mustang Fuel Injection Computer), by TMoss:
HTML/web version:
http://www.veryuseful.com/mustang/tech/engine/EECIVInnerWorkings/
PDF version:
http://www.veryuseful.com/mustang/tech/engine/EECIVInnerWorkings.pdf
A GREAT, IN DEPTH, Very Technical, Referance for the EEC IV. A MUST READ!:
http://www.veryuseful.com/mustang/tech/engine/eec-IV-Tech98.zip
More at:
http://www.veryuseful.com/mustang/tech/engine/