I purchased a 1979 928 last october...the car came from California and I live in Salt Lake City. When the outside air temp is 40 or below the engine seems to run fine...but the warmer the outside temp. the engine starts running rough and the exhaust sounds restricted...any suggestions on the problem and solution would be appreciated

 

Maybe one of the fuel pumps isn't working? Also could be Warm-up regulator. When it acts this way, is it blowing black smoke out the exhaust or does it look clean? Knowing that will help point you in the right direction.

 

exhaust is blowing clean

 

I second the vote on the WUR. There are several good write's up on re-adjusting them. I have a link on my website..