Vacuum replacement level
So, my story begins with the engine in my car starting poorly after a cold spell. It wasn't starting on the first try. I checked everything with a tester, replaced all the sensors, and also replaced the fuel pump and fuel pressure regulator, but the rough running problem persisted. Then one evening, it dawned on me: I went to start the car cold with the brake pressed, and lo and behold, the car started on the first try. The revs weren't fluctuating, everything was fine. As soon as I released the brake, the car stalled. The problem was a faulty vacuum system.