Undesirable Behavior
* Check Engine Light is illuminated constantly.
* ASR Light is tripped spontaneously with Limp Mode. This occurs occasionally on startup, but also occurrs every few miles at any speed.
* Engine Hesitation at low RPM. This occurs most noticeably when engine is cold and car is just beginning to move down the street at about 10mph. If the engine is warm, no hesitation is evident.
* Slightly Rough Startup. This occurs occasionally when the engine is warm.
* 3-4 Attempts To Start Engine. This is necessary if the engine has not been started for 5+ days. If the engine is not started for 15+ days, then it may require 10-20 attempts before it kicks over and starts.
* Very Rough Idle On Startup. This always occurs if the engine has not been started for 5+ days. It takes about 1-2 minutes to smooth out. The longer the engine goes without being started, the rougher the idle will be after it starts.
* Soft Backfire On Startup. This frequently occurs when the engine is cold, but is not loud and not easily audible.
* Uncombusted Gas Smell On Startup. This always occurs if the engine has not been started for 5+ days.
* Anemic Acceleration. This is most evident in the lower RPM ranges < 2,000rpm.
* Miserable MPG. The MPG has deteriorated significantly.

Parts Replaced
Recently replaced parts in this 94 E420 include:
Engine Wiring Harness
Spark Plugs
Caps & Rotors
Fuel Filter
Fuel Injection Temp Sensor Switch
Brake Lamp Switch
Neutral Safety Switch
Mass Air Flow Sensor
Battery
Valve Cover Gaskets
Oiler Tubes
Oil (with Valvoline 20W-50 Synthetic)

Note: Her Vacuum Pressure has tested fine. The MBZ Doctor has also checked the codes several times and is sure the problem with this 94 E420 is a bad ETA.

Possible Part Failures
I believe the problem(s), beginning with the most likely, may be as follows:
1) ETA (Electronic Throttle Actuator)
2) Fuel Injectors
3) Alternator
4) Alternator Wiring Harness
5) Oxygen Sensor
6) Cam position sensor
7) Wheel Speed Sensors {may need cleaning}

Questions
Would a bad ETA also cause the suspicious uncombusted gas smell (if engine sits for a week or so) on startup and accompanying rough idle?
Would a bad ETA cause terrible gas mileage?
Or alternatively, IS THIS AN INDICATION OF A FUEL INJECTOR LEAK causing a wet cylinder to develop when the car is not in use?

Over
DC