Runs rough after start
 

My 86 944 NA has been running rough for the first few minutes after start up. It doesn't do it all of the time, but when it does, it seems like it is running on 3 cylinders. After about 2 - 3 minutes, it smooths out and takes off perfectly. It doesn't seem to matter whether it is cold or warm, but it always happens after setting for several hours.

Any ideas?

Engine DME temp sensor.

Possible vacuum leak - the 20 year old rubber is probably brittle and cracked
The one under the intake manifold is a likely culprit because as it heats up (from sitting on top of the engine in a zero airflow area) the rubber will expand. When it cools back down the rubber contracts. 20 years of that will wear them out.

I'm not sure about a vacuum leak or temperature related issue. It could be, but this morning it was 28 degrees F and it ran rough for about 5 seconds and then was smooth as glass. It is definatly an intermitent problem. How do I check the altitude sensor?

Hey, let me know if you find the problem, mine does it too, but a little differently.
Mine, if it's below 10 degrees celcius (give or take) when you start it, it runs decently for about 5-10 seconds, then you hear it start to kind of stumble, then it comes back, but sounds like it's only on 3 cylinders until it has run for 5 minutes or so. If you try to rev it at all while it's like this, it is VERY sluggy (no matter how little or much you press the gas pedal, it takes about 10-15 seconds to hit 1500rpm). I thought DME temp sensor as well, but AFAIK, mine checks out (it did about 2 weeks before it got cold here, and it's been doing this since it got cold).

Could be a leaking fuel injector, one cylinder a bit rich.

It's a wonder these cars run at all!