THANKS for all the quick replies/advice. Some updated info:
The correct idle speed at operating temp. for DI engine is 500-550 RPM. Did you gap all the plugs? or just put them in?
You need to do a code reading
A little throttle body cleaning will help too.
Put a vacuum gauge on the intake and get some vacuum readings.
Gap plugs? Do people still do that?
I put new plugs in 30K ago. Can't recall if I gapped them, I doubt it. Can/will check again.
I don't have a tach instrument, but by ear / dash tach the idle hasn't changed in 6 years I've owned the car, tach dash sure looks like 750 but must be lower than that I am certain.
No CEL, no codes showing up on my $39 el cheapo code reader. What reader should I upgrade to please?
I sprayed/wiped the top and bottom of the throttle body and plate with throttle in wide open position 1000 miles ago - did not remove T Body
Put vac gauge on port to right of engine - the one that connects to intake hose - but negligible vac reading coming out of there at idle (1-2) . I searched but other than brake booster could not find another port/help?
You haven't stated which engine you have. Ignition coils are known to fail on these cars, a scanner will advise as to the extent that misfire is a problem.
Misfire is often a different problem from hesitation at throttle tip-in. It is possible you have one of these problems, or both. When you depress the throttle at low RPM, asking for moderately high load, and the engine misfire and jerks (low RPM high load is common regime to misfire) that would be a misfire problem, as opposed to hesitation where the engine doesn't respond immediately to throttle, rather it exhibits a delayed response, then surges. It is helpful if you can identify the difference, as the causes are different.
2013 CTS Luxury 3.0
Car has always had a very brief, slight, funny, single misfire feeling when applying the throttle at 45MPH or so. Not a hesitation, not a stumble, just the slightest of delay which always made me think of a torque converter lockup hiccup when in 6th gear doing to 5 or etc - nothing that I felt needed attention as it's felt the same for 6 years 80K miles. Maybe this is coming back to bite me, dunno.