How do you test an Idle air control valve?

Have a 1994 S10 Blazer with 4.3 liter, central port fuel injection. The motor idles fast. Can drive without touching the throttle. Get code 35 (IAC valve). Replaced the IAC valve, but still runs fast. Cannot find any vacuum leaks. Want to test if I recieved a bad IAC valve or have a bad connection.

A quick way to see if the IAC solonoid is working is to ground the test port under the dash, like your retrieving codes, let it flash its codes for 30 seconds, get under the hood unplug the IAC, pull the ground off the test port and start the truck. What this does basiclly is it resets and totally closes the IAC valve. If it starts with a high idle at this point, either your idle valve is not working, or you have a vacuum leak somewhere. If it does start or starts but dies, your IAC valve is working more or less.