IAC Spacer

I've got a '94 GT that idled at about 1500+ RPMs and would stall. I changed the IAC with one from AutoZone and it jumped to 1800+. I cleaned out the stock IAC with intake cleaner and put it back on. It idled normally, but the next day the idle went back up to 1500+ and it started stalling. I got another IAC from AutoZone and it went back up to 1800+. I saw an IAC spacer on ebay for about $20 that claims to fix idle problems. Has anyone tried one of these? Or am I better off buying a new Ford IAC?

I did some work on the engine (minor upper rebuild) and when I put it back together it had this problem. I had a Ford guy check for vacuum leaks and he found and fixed one. I called him after I bought the AutoZone IAC for more suggestions. He said to remove it and cover the holes with tape, which I did. The car wouldn't idle without me giving it gas. That's when I put the original back on. The throttle closes completely. I have double checked the screws. Looks like it's time to head to the dealer.