If you want a very detailed description of the problem behavior and what I have already done to try and fix it, you can look at some of my previous posts.
How about a link instead of making us search???
Specifically, my question today is if there is one (or more) temperature sending unit(s) that tell the ECM that the engine is cold or warmed up? Since it runs perfect once warmed up, it seems that perhaps something is telling the ECM that the engine is warm when it is actually cold.
There are two water temp sensors in the lower intake manifold. The 2-wire sensor is for the ECM. The 1-wire sensor is for running the temp gauge.
The Idle Air Control Valve appears to be working fine. The IAC has strong vacuum at start-up which decreases to minimal vacuum once warm.
You lost me here. An IAC is a computer controlled idle valve. The 2.6 doesn't have an IAC valve. And what do you mean by it has "strong vacuum"?
Cold idle is kicked up two ways on the 4Z. First is the Aux Air Valve. This is bolted underneath the intake manifold with a hose running to it and to the intake tube in front of the throttle body. When cold, it lets air pass and a bi-metallic strip heats (electrically) and closes it off.
The 2nd is the Thermal Valve. This is the tree looking valve on top of the t-stat housing. It passes air to the intake manifold when the water is cold, and re-directs it to the fast idle solenoid as the water heats up.
The fast idle solenoid then will open when you have the A/C on to kick the idle up again for that. I'm not sure if it's there though if you don't have A/C.
So, an idle problem when cold likely won't be an ECM/sensor issue. (I suppose it still could be a fuel/MAF issue though). It's controlled mechanically by the AAV and the TV. Both of these have hoses that run to the intake tube in front of the throttle body, so by doing a cold start and alternately pinching them and seeing their effect on idle, you should be able to figure out which one is not doing it's job.
--Dan
