This has been an occasional problem with my N/A 850. At any point within about 1 minute of starting the engine from cold (idling for about 20-30 seconds to get some oil flow), driving normally the engine shudders a small bit. Not necessarily feeling like a misfire. Just like it doesn't want to do anything above 2500 RPM. It's completely gone when the engine gets any temperature whatsoever and is really more of just an annoyance. I'm just making sure this isn't a common, easy to fix problem or something that could cause damage.
Thanks for any input!
-Luke

 

when was the last full tune up? sounds like the spark may not be hot enough or your ECT is a bit off.

 

New MANN air filter, New OEM Spark Plugs. I have no idea what ECT is...

 

engine coolant temp sensor. The computer uses the input to modify the mix based on engine temperature.

 

I have been having some issues with cooing as of late... The senor right underneath the thermostat correct?

 

yep. Good time to do the sensor, thermostat and the overflow cap. When I did my s40 I didn't bother to drain any coolant - lost about a cupful... not sure about the 850s so you may want to drain some coolant.