Won't Idle When Cold
 

Need to press accelerator and keep pressure on it to start car and keep it from stalling. Once engine is warm, all is well.
Any ideas?????

Colenzae,

I occasionally get this, but I have deduced this is a function of traffic, air temperature, altitude in my case, even after I clean every thing (IACV, MAF)...the latter two which I would take a look at the first based on the sticky that is at the top of the RX300 thread involving gas mileage.

When did this issue start for you?

Well, as you know last week I worked on the car, turned the rear camshaft one tooth to get the timing back to where it should be and eliminate the code for camshaft position sensor. I did have the throttle body off when I did this. The car has been running fine for over one week and about 600 miles.
This issue started on Saturday after driving for about two hours in very hot, humid weather. The car did sit for several hours before we went to start it. She won't idle on her own without keeping pressure on the accelerator until she's warmed up. Then she idles fine.

On the way home from that trip we stopped for gas and I put in high octane and a bottle of fuel injector cleaner and then drove the car for about 100 highway miles. I normally run 87 octane fuel. The next morning we noticed the same problem.

What keeps the cold idle on this car? Is it computer controlled or is it mechanical??

Call it a combination so to speak. Usually what I find it is the mechanical part, and I have to spray some carb cleaner through the hole on the right inlet of the throttle body to clean it. Now, some people do suffer a bad IACV valve and it has to have a combination so to speak. I always pull the battery cable after I get one of these funny incidents, usually on the ride home (and we also have been having hot, humid weather here), but often it self corrects after I get into less traffic. A possibility here, is that it was just long enough in this weather pattern for the sensors to register it as part of your driving pattern. Only other time I know of this strange behavior is in vapor lock situation (dealt with this once when driving it down 8,000 feet to Veracruz) and next morning it was tough to turn over the RX.

Reset the computer but that didn't seem to work. Still wouldn't idle when cold.
The next day however, the problem seemed to disappear.
Weird. I'll see how it goes over the next week or so..........

After pulling the battery, this happens to me, and I also have to give it some gas until the idle comes up. This is because, for lack of a better description, the vehicle's ECM has no idea about the outside world (air temp/speed) until its sensors kick in a few seconds later, and even after that it takes a cit until a full drive cycle is deteced, something that can be checked with some OBDII Scanners (engine readiness).

Sounds like your IACV is going, I would replace it if you've already tried cleaning it.