Having a problem with cold starts on 2001 Lexus ES300. How do I check(and replace) the IAC valve(and where is it located). Also, what to use and how to clean the throttle plate.

Here's the removal procedure. The IAC is located at the bottom of the TB. 4 screws hold it in. Pay attn to the order of the hoses removed from it. Paint mark them to be sure they go back right. Be gentle in twisting them off.
Make a mark on the throttle body gasket also to prevent it being put back on backwards. A very common rookie mistake.
Replace the gasket with the new IAC.
Clean the trottle body while it's out of the car on a bench with rags to soak up the cleaner.
Use "Throttle Body Cleaner" from the parts store or dealer where you get the part. Not Carb clean! Top off any spilled coolant
Drive vehicle a while to relean idle control values.
Good luck. Here's the file below.
Attachment 28487