Subject: What does the throttle body spacer?
Question:

I got a mitsubishi eclipse 96 gs spider 2.4 and I've been having problems with the idle, i took it to the mecanic and he told me it was the thottle body unit. Can be the whole thing?. Can be the idle air controller, o the TPS(throttle position sensor)? o what else can be?. 

Answer: Guillermo,
Replacing the entire throttle body is typically not performed unless the unit is physically broken. You are correct when you mentioned the possible cause as being the idle air controller or the throttle position sensor. The problem could even be the fast idle air valve or even just a warped throttle body gasket. I'd recommend getting a second opinion and find a new mechanic. A new throttle body would cost $500-$650, so get a couple opinions if you don't feel like spending that much.
Good luck!