08 GT 190,000 miles. What is with this erratic/searching/stumbling idle I get at cold start up, but runs fine when warm? New Motorcraft plugs, everything else, original stock. Did it before I changed the plugs.

 

Could be a number of things. I always start with the simple stuff: clean the TB, clean the MAF, run a tank or 2 of SeaFoam.

Are you stock? If not and you're tuned, have you swapped tunes to see if it continues?

 

Simple Diablo Predator 93 octane tune. Also, I don't get the concept of a dirty TB and only doing it when cold. Just cleaned the MAF. Are there sensors that read the coolant temp and communication that to the ECM?

 

Faulty Cylinder Head Temp Sensor cause this problem?

 

These cars are very sensitive to any air flow changes. A dirty TB will causes issues. Buy some cleaner specific for the TB and clean the crap out of it. The MAF will also get dust built up on it and eventually not read as well as it did before. It will only cost $10 for this maintenance.

When it fails it will read all the way hot or nothing at all. At least that's what I found when mine failed. My sensor didn't fail, it was the wire going to it.

 

When you clean the TB, make sure you remove it and use lint-free rags.... The PCV system has so much blow-by it's disgusting... It was worse with the supercharger, hence why I went to breathers.... 3k miles now and no oil buildup on the valve covers (yet)

 

I would say plugs, but you changed them. How are your coils? Also, clean the tb and maf.