3.0 Warm Engine Problems
 

I have a 1980 3.0 with it's original CIS system installed in my 74 911. The engine runs great if I start it when it's cold, if I start it after it's been warmed up a bit it runs pretty poorly. Generally after starting it once it's been warmed up it idles lower and is lacking power, it also seems to cough a bit for the first 10 seconds or so. Any ideas would be helpful.

Thanks,
Dan

First step is to check control pressure hot and cold. You can buy the required gauge from JC Whitney for ~$50.00. Plenty of info around here.

Is there any particular issue that would cause this, I'll work on getting the pressure tester but in the meantime is this a common CIS (with oxygen sensor) problem? Is it likely an issue with the warm-up regulator.

If the car starts up from cold it will run perfectly for hours, if I shut it off for a few minutes to an hour or two and restart it it will run poorly?

Can the warm-up regulator from an earlier (1978) CIS system be swapped out for the one on my car (a 1980 unit)?

Checking the pressures is the first step.
While checking the pressures you will discover that the fuel pressure at rest is bleading off. Check the fuel pump check valve and the fuel accumulator. Both items can bleed of pressure while the engine is at rest.