My Roush does that also, when it has sat for a period of time when its cold. Its not a issue with the engine. Its to prevent the engine from any damage. Let it run like that until it comes up to temp. My car the RPMs jump up and down like it has a governor on it. it take mine about 20-30...
2022 Roush SC serial number 1 of 15. 6900 miles.
Bought new, had to wait 2 months for Roush performance in Michigan to finish installing components. Had it shipped from dealership to house.
Heck with wasting all that money for a simple equipment violation. Regardless of law never will put anything plate related on front of car. Violation doesn't even go against insurance.
He did mention it was a pass thru so that makes sense now. I just reflashed tune when he was done. Just started it and let it run, but didn't drive it. I didn't notice any issues.