[s-cars] Part-throttle hesitation when cold

[Erik Addy]

So, back to Ur-S conversation, right? :)

When cold (not ambient, rather when the engine is not warmed up), the ur-s now has a part-throttle, off-boost hesitation.  Ignition is the LS2 kit from EFI Express (great kit, BTW), so I don't think ignition is the problem (although I suppose a bad knock sensor could do it).  I'm thinking fueling, so what to consider?

Fuel Pressure Regulator?  It would make sense that when the car is cold and runing open-loop that the FPR could cause a problem.  Then when the car goes open loop the O2 sensor could trim the fuel and solve the issue...

Coolant temp sensor?  If the ECU didn't know the engine was cold.... The coolant gauge reads as it should, is it a different sensor or different output from a MFTS to the ECU?

Any other suggestions or input?

Thanks
Erik