300E'89 Aiir flow control valve?

[Gunawan]

Hi everyone,
I just join as a member on this site. I have a problem with my 300E with 103 engine. It is an asian model ( might be similar to european model), right hand side steering,and have manual transmission.

The simptoms are:
1. The car starts ok when cold (in the morning). When its warm the idle seems to drop, and often the engine died during a turn, or when the a/c on or the lights on. And if I start it again the engine is on and running, but the idle rpm is low.
2. When stops and idling the engine sometimes got almost dead but then the rpm suddenly jumps for a moment (maybe the control kicks in late)
3. A/c idle up is not working when the sickness come.
4. When driving on low speed and want to increase, the power sometime hesitant.

The mechanic said it is the Air flow control that is faulty, and then whole assy cost $500. I want to know for sure if it was the faulty part before I pay that much money for this old car.

By the way :
1. I checked the OVP and it looks clean, smels normal (nothing burnt)
2. ABS light not on.
3. Changed spark plug, ignition coil, rotor, distributor, spark cables.
4. Changed fuel filter.
5. Changed one of the fuel pump (it was leaking before)
6. Changed the small filter/strainer on the fuel dish housing.
7. New battery.
8. Alternator assumed good because of sufficient charging of battery.

Can anyone help me?
Is the mechanic said the truth?
Is it maybe the O2 sensor, and where is it? (we dont use catalytic conv. in Indonesia).
Can I replace parts of the Air flow valve control, and not the whole assy?
Thank you much and pardon my English.
Bye.