2001 C240 45K Miles

Removed top covers, saw breathers and valve cover have unusually large leaks for this mileage. Clearly leaking into plug wells on both sides.
Replaced covers,
Removed oil cap (clean, not milky) and radiator expansion tank cap, started car. I want to see if anything is churning and bubbling. All is well, re-capped both.
A short roady
Hooked up iCarsoft and No engine codes.
Another short highway roady and it threw a CEL and bad idle.
By now I am not around and so I don't have a code reader.
Could any of this have caused this issue? If not could it be that the leaks caught up with it?

Probably more vacuum leaks you haven't found yet. Make sure the MAF and elbow is properly installed. It's easy to get it wrong.

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CENSORED due to not family friendly words

Have the codes read and report back.

Sixto
98 E320 sedan and wagon

Your ECM will shutdown a cylinder if its detected in misfire (it watches the crank sensor accleration cycles to determine what cylinder is firing unevenly)

It results in a real bad idle and extremely worse if you have 2 cylinders shutdown.

Usual cause is worn plugs and bad plug wires (12 plugs and the rear most are a pain to do) check wires with a multimeter first and then with a spritzing of water while engine is running.

btw - I hope you used a real good sealant on the breather covers as all store bought ones leak after a month or so, the only sealant that works is genuine MB black silicone or loctite 5800, toyota black sealant or threebond 1207B or General Motors gray engine sealant (i love this stuff as its cheap and has excellent sealing properties)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)