My W202 C180 (1995, 105,000km, M111 engine, 4-speed auto transmission) has been stalling once it reached 100,000km. Initially, a few time each day. Now, about once a week. After turning off the ignition, it would run OK.

The following has been changed/performed:
1. New spark plugs (Bosch Copper), Fuel filter and Air filter at 90000km;
2. New fuel pump, fuel pump relay, and OVP once the problem surfaced;
3. Fault code read and re-set: persistent code 021 (idle speed control in emergency operation. Speed control actuator.) Intake manifold pressure 390 mbar, O2 sensor voltge 1050 mV

The engine was only idling at 400rpm (air-cond on, auto transmission at "D"). with the air-cond off, idle at 600-700 rpm. The next day, the idle was OK, but it continued to stall about once a week.

After going through the thread on this site, I disconnected the air flow meter boot and cleaned the throttle housing and throttle linkage with carburettor cleaner. The throttle felt smooth for a week, and then the stalling recurred.

Is there anything I should attempt, before purchasing a new Throttle Housing (000-141-9125)?

Thanks.