2001 996 tip 74k miles

Here's the story: on cold days (it does get below 40 in Los Angeles) my car starts, jumps to around 1200rpm, down to about 600 shuddering, up to about 1200 again after about 10 seconds, then back down to about 800 shuddering. After about a minute of driving all is fine.

Here's what I have done after lots of searching:
cleaned the MAF (looked new)
cleaned the throttle body
car just had plugs about 10k miles ago
ignition coils look fine
code reader reports nothing

What else is possible?

 

Did it just start acting this way when cold, recently or can it be linked with bad gas? Any mods to the engine? Can you hear the secondary air blower start when cold? You might try removing the MAF connector and clean the contacts. Add a bottle of injector cleaner to the gas tank. Disconnect the MAF cable and see if you get the same symptoms. Before starting the cold engine, first warm up the coolant sensor (located on the bottom right, bumper side of the engine) with a hair drier.

 

Injector cleaner has been done. forgot about that.
Although this has only been happening for a couple of months, it's only been cold for a couple of months.
The only engine "mod" is a Schnell cold air intake.

 

coolant temp sensor. try the hairdryer trick, i never heard of that but sounds like it could work.

 

I have an EVO intake and cleaned it once and reinstalled without reoiling. It ran like crap and blew a MAF. I oiled it and let it sit overnight and runs much better since. Do you have the stock airbox?

You can try changing it back to stock and see if that solves the problem. I was surprised how sensitive our cars are.

 

Airbox and filter are stock with he exception of the airbox muffler being removed.

 

OK, replaced the coolant temp sensor $14 and 10 minutes labor.
No luck. What next?