1998 Chevy Camaro hesitation whencold

Horrible fuel mileage on this car can be attributed to two things, a yong kid with a heavy foot or something wrong with the engine. As you are not getting any codes and it acts up cold that's a hint that it's a basic problem. I"d check for a vacuum hose off or soft and leaking. When its warm the computer is trying to compensate for the vacuum leak-hence richining the mix letting car run ok but giving poor fuel mileage. That is the first thing i'd check for is the vacuum leak via the hoses. After that have the engine scanned again someting may come up.

A couple of things I forgot were to change teh fuel filter as you just got the car and you don't know when it was last changed, and take the air duct off and take choke cleaner and clean the throttle plate on both sides as they tend to gunk up with oil and then stick closed and operate poorly. Also check the air duct for holes between the throttle plate and maf sensor.

Another thing if you can get a vacuum gauge on it is to check vacuum at idle. If it's around 15" you'll have to check for a plugged converter. It should be around 20" also while the throttle body is noisy, spray some choke cleaner around it as it may be leaking at the throttle shaft.