2008 C350 Turns on but dies right after.

Any help comments suggestion knowledge would be so appreciated. So I’ve had my car for about 5 years and never had a problem until I took it to get an oil change at castrol premium lube express. After the oil change they could not start my car. I was forced to leave it their and the next day they had their mechanics take a look. I was told their scanner had this code p2004 tumble flats intake manifold stuck in the actuated position. Was told they plastic part was broken so they would replace it with a aluminum or metal part. I agreed to the service and the next day was told that the car will only turn on by putting it into the on position then back off then on position then back off then on position then back of and on the 4th try turn the key all they way. I said well my car is not fixed then. Long story short I took my car went home then drove to work that night (I work graveyard) and my check engine light came on. I’ve never had a problem or a check engine light come on. So now my car still won’t start until you play with it for 5 minutes and I also have a check engine light on. Any suggestion what it might be or what I should do? I would like to avoid the dealer because of price so any Help is big help I can’t drive the car like this it’s frustrating and I’m afraid one day it will stop turning on. Thanks in advance and sorry for the long post but I wanted to make sure I explained myself.