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That rpm instability at idle is classic vacuum leak symptom.
Pulling codes is almost always step one. Your local parts store will usually pull codes for free. The cheap ~~$10~~ $5 Bluetooth readers on Amazon, plus the free app "Torque" work well for the price.
I keep one of those readers in every car and install Torque on all our phones.
I was going to say vacuum leak too. Get some brake kleen or other flammable liquid and spray judiciously near different parts of the intake while the engine is running and listen for a change in idle to help locate it.
Note: spray flammable liquids at your own risk. If you don’t know the risks and what to avoid have a mechanic do it.
Yep, this found many bad carb gaskets for me.
You want to check downstream of the MAF sensor (the electronic box thing a little larger than a pack of cards).
Thanks all, already went by my mechanic once to get the codes, but no engine light or error was present just as i started it then 🥲
Will try again next time I ger the light.
but no engine light or error was present just as i started it then
Haha, of course it wasn't! Classic.
There's a few c-max forums you can check. Pulling codes would be helpful. There's a program called forscan for fords that will give you a lot more information than a basic scan tool. I saw a few threads where people had the same issue but no resolution. Just don't fire the parts cannon at it like one guy did. There's lots of things it could be. You might just do a quick visual check to see if anything looks off. Make sure the airbox lid and hose are on correctly and tight. Check the vacuum hoses and look at the throttle body connector. It has an electronic throttle, so the pedal couldbe messed up somehow too.
Lots of things that could cause rough idle. Vacuum leaks and spark plugs are common culprits. Dirty/worn spark plugs are often accompanied by unburned fuel or soot in the exhaust.
You'd have to put a vacuum gauge on the intake manifold to check for a vacuum leak.
Beyond that, you'd have to check the diagnostic codes to see if it shows something else amiss.