I recently upgraded the Terminator ECU from V2 to V4. Since then, when the engine is cold, it idles well but, if I raise the RPM (even slightly) and then get off the throttle, the engine almost dies. The RPM drops down below 600 (normal idle is 800), it stumbles for 3-5 seconds, and then I hear the IAC open up and it returns to normal idle. It's as if IAC operation is being delayed. I seem to recall this happening with V2, but not to this extent.