you may have more than one coil misfiring and when they replaced only one coil the other ones went undetected...

do you know your exact codes logged in the computer? i've had similar issue with a coil, that logged all kinds of faults but one of the faults was consistent, that was coil #5 and variations of that cylinder... i also put the INPA (software that can program and monitor live motor data) into cylinder roughness test and let the engine idle - while engine idled OK, i noticed some changes in the sound of the engine, that never bothered me before - until i was able to correlate those "rumble-rumble-rumble-rrrumble-rumble-rumble" to the live view of cylinder #5... that extra "rrrrumble" was matching "nervous" movement of #5 graph bar... it made me think, that the coil #5 was not doing well, even without any load, and with the load it was just dying...


after i replaced the coil, the engine idled "rumble-rumble-rumble-rumble", without any extra "rrrr", and all the problems were resolved...

in your case, you may have more than one coil acting up and ALSO the spark plugs being fouled up...

I would not have taken the car to a dealer for the simple things such as coils, as they will diagnose the problem and throw parts at the car in hopes to fix the issue - AT YOUR EXPENSE...

you can get BOSCH coils on line (check ebay), and replace all of them yourself... spark plugs might be a bit more involved but still, doable...

try to get the actual read-out of your error codes, and if you are still taking the car to the dealer, see if they will let you see the live data - if they even check the live data...