Rough idling engine in traffic, will cut-off in heavy traffic with A/C. on 2000 Mercedes-Benz S430

rough idle in bumper to bumper traffic with A/C on, will stall occassionally in heavy traffic. New plugs and wires have been installed. No check engine or malfunction code given.

Asked by for the 2000 Mercedes-Benz S430
I would have thought you would have a check engine light but even so a professional grade scan tool attached to the diagnostic socket under the dash would give data on air fuel ratio to indicate a vacuum leak or not, it may also be able to operate the idle air control motor and see if it would operate properly, it's hard to say what exactly is wrong without being able to do basic diagnostic tests.