Ok... I had no idea what you meant by rocket... that was a typo on their site and they meant rocker... not entirely accurate, we don't have rockers... it's more commonly called a cam or valve cover. Yeah, it's not uncommon for those to leak as the seals leak and the screws back out.
The bypass to which you refer is the idle speed controller... It is not uncommon for it to get clogged up with oil and dust over the years and as a result it may cause iddues with the idle.
As your valve cover are leaking I would first pull the spark plug wires and check if oil has leaked down in around the plugs; it's just as common as the leaking valves and can cause shorts.
To check for diagnostic error codes you simply need to install a jumper and count the flashes of the check engine light.... very easy and cheap. I'd start with that before paying Toyota techs to do it. :P
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
If you're even subtly mechanically inclined I'd just replace the valve covers myself as well... the hardest part is disconnecting the throttle body (a whopping 4 bolts
). Wehn tightening the screws that hold the valve covers use some light strength thread locker and don't over tighten them.... they really only need the be a firm hand tight (just under 2 ft lbs or 2.71 Nm).