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Old 10-14-2001, 12:44 AM
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Join Date: Nov 2000
Posts: 107
Question How to Clean or Maintain Throttle Valve Actuator on 1994 E420

Just wondering if there is a set procedure for either cleaning or maintaining the throttle body actuator in a 1994 E420. I would like to make sure I have done everything possible with it before plunking down big bucks to replace it. My car has had a combination of three problems which may be interrelated:

1. The car hesitates ever so slightly when pulling away from a stop. The problem is more pronounced when trying to back up a steep hill. The car actually creeps forward (downhill) until all of a sudden, the car accelerates, many times causing the tires to squeal.

2. The car stalls occasionally when hot and idling in heavy traffic.

3. The cruise control spontaneously disengages after 10-15 minutes of normal operation. Usually, I can just set it again, and it may work for another 15 minutes or so before quitting.

Benzmac suggested in a private message that all of these problems can be solved with a new throttle valve actuator, but I just want to make sure that there is nothing I can do to the old one before spending that kind of money. I recently swapped out the air mass sensor from an identical engine, which seems to have helped out the stalling and hesitation problems. I have not had a chance to try out the cruise control though.

Any assistance is greatly appreciated.
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Old 10-14-2001, 02:23 AM
94 E320
Join Date: Jun 2001
Location: Fairfax, VA
Posts: 437
if thats what Benzmac says believe it and trust it!

if there was anything else...the man would tell u

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Old 10-14-2001, 05:25 AM
David C Klasse's Avatar
CheFrac is Back!
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Location: Mission Hills in the City of San Diego
Posts: 2,352
Re: How to Clean or Maintain Throttle Valve Actuator on 1994 E420

Originally posted by screedchan

I just want to make sure that there is nothing I can do to the old one before spending that kind of money [on a new one].
Understand now?
2006 E350 w/ 155k miles (Daily Driver)

1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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Old 10-14-2001, 10:50 AM
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Join Date: Nov 2000
Posts: 107
As I understand it, the throttle valve actuator is a device that opens the throttle according to the position of the gas pedal. Is the collective wisdom of this forum that the minute it acts up, it is an automatic replacement? Benzmac suggested that these often require replacement when the small wiring harness is degraded by heat and age. However, the harness on my unit looks okay, so I just wanted to know if there was anything that could be cleaned or maintained apart from the wiring harness. Perhaps I might garner more helpful responses with this additional information. Thanks.
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Old 10-14-2001, 10:55 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Its my understanding that MB has redesigned the internal potentiometers and switches. I don't think there is any way to repair.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 10-14-2001, 10:57 AM
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Thanks Steve.
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Old 10-14-2001, 11:47 AM
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I guess the key here is discovering what are the typical failure modes for these units, as well as the specific failure mode for any individual one unit.

I will need to be dealing with this issue myself, although I have not yet actually done a physical inspection of the throttle actuator that is on the recently acquired 94 E420.

If the failure consists of deterioration of the insulation on the external wiring, perhaps that can be resolved in a rather straightforward manner. If the internal potentiometers and/or switches become fouled or dirty, perhaps disassembly and cleaning with the proper solvent (TV tuner cleaner?) may work. If the traces on the potentiometers are worn through, then you're pretty much screwed. Once again I have to state I have not actually looked at the unit yet, so I'm flying blind here -- disassembly & reassembly may not be practical.

And because we live in such a litigious world, I guess I should state the obvious. This is a highly critical part; failure could have dire consequences, therefore any attempts at repairing these units would of course only be done for the purposes of testing the theoretical feasibility, and of course the ‘repaired’ unit would never actually be used on an engine that is actually installed in a car.

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Old 10-15-2001, 06:44 PM
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Join Date: Nov 2000
Posts: 107
What is the forum members' collective wisdom on using a used throttle valve actuator? In checking with Phil at the PartsShop, I learned that this is a dealer only part which lists for $950.25, although Phil was kind enough to pass it along for his cost, which is still $800 or so. I found a used one on the net out of a 95 E420 with 57,000 miles at a cost of $275. Is this a common failure at 120,000+ miles, or is it only the odd bad apple which goes out. If it is the latter, I would be inclined to try the used part, while if the former, my decision gets harder.

Anyone out there have a feel for how often the throttle valve actuator needs to be replaced? Thanks.
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Old 10-15-2001, 09:54 PM
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Join Date: Mar 2000
Location: Outside Indianapolis, IN
Posts: 214
My 94 E420 has an odd intermittent problem that may also be the actuator. The engine rpm surges occasionally (or maybe the throttle isn't closing quickly enough?), most noticeable upon deceleration and braking, but occasionally at idle. It is VERY disconcerting but brief, to have this surge when I'm trying to stop, or at idle in the garage or a drive through. I noticed this after cleaning the throttle body. I've replaced the rubber sleeve that attaches the mass flow sensor to the throttle body and the car has had both upper and lower wiring harnesses recently replaced. Any thoughts?
Bob Johnston
03 E55
Comand/Nav/Bluetooth/Ipod added
(Oh man, this car is sooooo fast.)
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Old 10-24-2001, 11:12 PM
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Join Date: Jul 2000
Posts: 638
wiring failure in electronic throttles

Based on my research (opening up several in the 'core pile' at a good local independent), what fails in the wiring insulation.

I guess one of the resistors in the matching network could shift in value and result in the voltages being off enough to cause 'limp in mode' to set.
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