Changed the valve cover and plugs, now the engine light is on

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I replaced the valve cover and spark plugs on my granddaughters 1.8 Sonic today, then flushed the radiator and added new coolant. The pcv was shot on the old valve cover, and since I didn't know when the plugs were changed last, I put new AC Delco's in. She told me it had a newer coil pack in it, so I didn't change that. I will say that the orange thing you push down on to unplug the coil was brittle and cracked. It fell apart when I was unplugging it, but a guy on a youtube video said that was common and to just plug it back in. I also wrapped it in some electrical tape to keep it from coming out. Anyway, she got back up to St. Louis and just texted me and said the engine light is on. Everything went well on the work done today. If anybody has any suggestions or comments on this, I'd appreciate it. I feel sick thinking my granddaughter drove an hour to let me fix her car only to have it mess up on her. And she works and is taking college classes, so she really needs this car. Aside from the pcv leak,and sounding like something's whining somewhere, it was running ok before today. Thanks for any help on this. Lee

 

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In case anyone has read this post, I was told by my granddaughter that after someone scanned her car, that it's leaking air into the engine somewhere. I'm heading up to St. Louis (where she lives) on Saturday and I'm going to pull the valve cover back off and check the mounting surface on the head to make sure it's got a clean, tight seal. Since I was interrupted twice when I was in the process of putting in the new cover, I may have failed to clean up the face the gasket sits on. Maybe. I don't know if that's where the air leak is, but that's my only guess right now.

If anybody reads this and may know of anyplace else to check for leaks, please let me know so I can be ready to check other spots when I go up Saturday. Thanks for any and all suggestions or ideas.