Rami

Dear so my car is tuned and runs beautifully at first then the next day I started it up and the car struggle to maintain cold start rpm fluctuate And bounces all over then it settles and when it’s warmed up I drove it seems fine until I want to down shift or if I pressed the clutch the car stalls or feels it’s gonna stall can’t find any vacuum leak and now it’s idling on 500 rpm for some reason can someone help me