The brief
The A180 was rough at idle, would stall occasionally when stopped at the lights, accelerated sluggishly off the line, and had the check engine light steady on. Four symptoms all converging on the engine's air-control side.
This engine has a variable valve-lift system, Mercedes calls it CAMTRONIC, that lets the engine switch the intake valves between two lift profiles for low and high load. It is moved by a small solenoid on the cylinder head. When that solenoid jams, the engine is stuck with the wrong valve lift for the conditions, which throws the breathing out and gives you exactly this: a lumpy idle, the odd stall, and weak pull away from a stop, all with a fault light to confirm it.
The diagnosis
The scan named the part directly: the CAMTRONIC intake solenoid for the cylinder bank was jammed in the ON position and could not return to its rest position. That stuck solenoid was holding the valve lift where it should not be, which matched the rough idle and the poor acceleration exactly.
A bench test of the solenoid out of the car backed it up, it was sticking and would not move cleanly. There is no freeing up a solenoid that has seized, so the fix is a new one with a fresh seal.
The work
The harness was disconnected, the jammed CAMTRONIC intake solenoid removed, and a new Mercedes-spec replacement fitted with a fresh seal, then the harness reconnected. The stored fault codes were cleared on the scan tool.
The live data was then checked to confirm the solenoid was now moving through its range as it should before the car went back to the owner.
The outcome
Idle smooth, no stalling at the lights, throttle response sharp off the line, and the check engine light cleared and not coming back.
The A180 went home running cleanly again. For the owner that is the end of the stumble at idle and the hesitation pulling away, and a small, contained part fixing a fault that had been throwing the dash light and dragging the engine for a while.