Stutter after preventative maintenance

Hey everyone, first post but definitely not new to cars. I know it's been talked about but couldn't find a relatable thread.

Purchased a not-so-new 2010 with 197k on it. It all started after I did some preventative maintenance. I changed the spark plugs, PCV, and pulled the EGR and the cooler to do the maintenance on those. The cooler was 100% blocked so instead of dealing with that I changed the cooler and the EGR valve. I also removed the pipe going from valve to the intake manifold and cleaned that. I removed the intake manifold and paid particular attention to the small holes and sprayed them with cleaner and blew them with compressed air. I put everything back together last night and eventually I was able to start the car. I let it idle and waited for the car to warm up so I could add new coolant. I took the car out for a small test drive and thought everything was good. When I was cruising at 45 miles an hour with a small engine load it would stutter. Under full acceleration everything was good. I figured maybe something was going on with the spark plugs because it was seeming like it was a missing and finally after driving for a little while the check engine light finally came on. It threw up error codes for mass airflow sensor, intake air temperature, and all the coils. All of those are connected. In doing all this I also noticed the oil was low by about 1.5 qts.

Am I dealing with EGR problems and need to pull the intake again? By chance, did I miss a connection and have no idea? The gaskets on the manifold are still original but not making any noise.

Thanks everyone!

 

I did. I could try to use the old valve to see if it's perhaps defective.

 

Alright. More to the story.

Took it apart again. Replaced coils due to a nasty misfire on #1 & 2. They were original - no change.

Decided to go after intake manifold again. Found I missed the gasket on one side where the EGR pipe comes off and goes to intake manifold. Fixed that. Removed manifold. MAP sensor is oily so I hit that with electronics cleaner. Passages 3 & 4 are gunked up. Tomorrow I will take them to work and clean everything in our parts washer.

Would a bad or dirty MAP cause the misfire and stuttering? And a "loose" pipe from the EGR?

 

Well,

Here's the deal. The manifold still had lots of liquid and solid bits of oil inside the EGR runner. I cleaned that out several times with MEK substitute. That removed so much junk. Huge improvement just in looks after that. I came home and put that on.

From last night's escapade, you'll read that when I put the pipe on the EGR valve days ago, the gasket slid sideways and I missed that. Vacuum leak / egr (metered air) leak. I fixed that tonight.

Connected all previously removed parts and plugs and took her for a spin. What a difference!! Maybe it's me but it feels so much smoother now. The highway drive will be tomorrow.

So, I feel stupid for the gasket, but thankful it's back. Now to monitor the oil consumption.

 

With all the garbage that went through the engine while cleaning (seafoam mostly) and running it with that stuff messed up, I have a P0420 code. Are we betting oxygen sensor or catalytic converter?