At red light engine seems like it wants to cut off.

Got an oi change,one week later check engine light came on,checked oil level it was low.took it back to shop explained what happened and asked why oil level was low when i just got an oil change.they checked and could find no leaks anywere,so they added oil,they gave it a diagnostic test and found nothing,only a few maybe this or maybe that.than they checked the manifold and said the oil distribution was not correct(bad cylinders)drove away got home and i lifted hood and pressed the oil reset button.a couple hours later the check engine light went off.thing is first thing in morning i start the car and drive abot 30 miles an hr.while stopping at red lights the engine seems like it wants to shut off but it never does.know if i put the car on the interstae and go 55 to 65 mhr for awhile than do city driving and stop at red lights the engine stays strong.sometimes the car has a knocking sound and sometimes it does not.it has been over a month the car still runs and it has never stopped.i have had the fuel system flushed,put a new battery in,put motor koet additive in ,started useing a higher grade of fuel.the check engine light has come on again but i just press the oil reset button and the light goes out.the check engine light only comes on when i do city slow driving and make a lot of redlight stops.after interstate driving engine stays strong and check engine light does not come on.can anyone help?with this economy i really do not want to buy another car.the car has 69,000 miles i don't drive it that much.i'm a truck driver and am on the road most of the time.help!thxs!