Rough Idle Questions-Need Suggestions
 

I recently purchased my first Porsche, a 1981 911sc coupe. So far, I love the car, however I am starting to experience some issues with startup/idle and a bit of rough performance at speed.

-On ignition, the engine sometimes sputters and seems to have a hard time catching its idle. (this doesnt happen every time I start the car)
-On ignition, the O2 dash light comes on, and stays lit until about 15-30 seconds after ignition.
-On ignition, a blip of the throttle is sometimes met with throttle hesitation and more sputtering.
-On ignition, my garage has a slight odor of it running a bit rich.
-While driving, there is a bit of backfiring when the vehicle is decelerating. (like when slowing down for a stop light, but still in gear)
-While driving, occasionally a slight feeling that there is a loss of power, when not under moderate/heavy acceleration.

A bit of background on the car: The engine was rebuilt about 40K miles ago, and the Cat was removed prior to my purchase.

I'd love to hear advice on what I need to start looking for/testing to determine the cause.

Thanks, I'm looking forward to many many miles of smiles with my new Porsche!

To begin with, you'll need to find out what else was removed or disabled in the engine. Seems whoever rebuilt the engine may have done more than just a rebuild. Look for things like disconnected or plugged vacuum lines and hoses etc.