I have a 300SE 2.8l (European Model) being used in India, which has run only 25000 miles and has been immaculately maintained. For the past year I am struggling to fix a simple problem. The engine does not idle, it hunts and stalls. I have carried out extensive and expensive checks and repairs and replaced parts as suggested by two repair shops.
Complaint :- 1. Engine Hunting (Idle RPM fluctuates violently)
2. Stalls when accelerator released.

Jobs carried out :-

1. Wiring Harness MAF SENSOR (MASS AIR FLOW):- Wires frayed, hence new wiring harness fitted.

2. HOT FILM - MAF SENSOR :- H.H.T. (HAND HELD TESTER) showed MAF sensor defective - Same replaced.

3. CONTROL UNIT - All wires and the connector checked for loose connection - found all ok.

4. CYLINDER HEAD - Valve grinding job done with new valves and gaskets.
Note:- Inlet manifold rubber rings were leaking - Same was replaced.

5. REGENERATION VALVE - Valve & pipe tested - found ok.

6. ELECTRONIC ACCELERATOR ACTUATOR - wires of actuator frayed - Hence same replaced.

7. AIR PUMP - Valve and hoses replaced.

8. SPARK PLUGS - Replaced with correct plugs.

9. INJECTORS - Serviced (All 6)

This car does not have O2 sensor and there is no provision for fitting it in exhaust pipe.

The CO adjustment potentiometer was disconnected - Same has been connected to Pin No. 23 of control unit.

At present the H.H.T. is not showing any defect but the engine is still hunting.
The computer is functioning, vacuum leakage is also checked.

Any suggestions welcome. Thanks very much.....Dipil(Exasperated)

Sounds like you have a very lean fuel mixture, you need to do a fuel pressure check and fuel rate check.

Thanks Ozzy! Already checked the pump even switched with a running car, no luck. Dipil