Okay guys I just got done working on a 2000 Civic EX D16Y7 with is code in it and the following problems. Car was stolen about a month ago...figues it's a red Honda Civic lol...They blew the engine and wrecked the l/r quaterpanel. When the new/used (around 60,000 miles) engine was installed it didn't want to idle right....This was done by a shade tree mechanic service btw. The idle was jumping between 750 to 1500 rpms. Also it had the code P0505 which is "Idle Control Malfunction". The code states to check you run the rpms at 3000 untill the coolantt fan comes on. the coolant temp shold be aroung 200 degress at this point and TP angel should be 10 %. Now all this was in line. Next it says to pull the breather hose and air filter out and look at the throttle body. If the rpms arebelow 550 you shold check the IACV. Unplugging it is the best way. If the car shuts off or dies it's good and you should adjust the IAC screw. Now since my rpms were above it says to place your fingers over the lowerthrottle body port with the car running. If the rpms drop then you move on with that step. If they don't you check the IACV. Thelowere port is is the elongated port, not the round one. I placed my fingers over the port and the idle stopped jumping. It then says to check for a vacume leak. SoI started looking. Turns out there is a vacume port on the lower side of the intake manifold on the left hand side of the car. It's very small. Plug that off and I fixed the proble. The car is running food now but I'm still not sure what that vaccume port goes to. Sorry for the long post just thought it might help someone.