1998 ES300 78k miles

About a month ago, the car would not start unless I gave it gas as I was turning the key. Once started, the engine would stall if I let go of the gas. Previously there was no sign of trouble, and I mean no sign at all it ran/started flawlessly. Had the car towed to a Lexus dealership, which ended up replacing the Idle Air Control Valve.

Ran/started fine eversince, up until yesterday morning when the same problem resurfaced. The only difference being that the engine will not stall now, but, just as before, it won't start unless I give it gas.

Obviously going back into the dealer to sort this out, but before I do that, I would appreciate any insight from any users experiencing similar problems or maybe even a mechanic browsing these forums. Thanks in advance.