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92 400E, 03 ml350, 1994 E420
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21 Posts
Discussion Starter #1
I have a 1992 400E with ASR, that is going into limp mode. I get a 2pulse code on pin #7, the code can be cleared but comes right back. The ASR light on dash stays on and the car stays in limp mode. the cars wiring harness was replaced. i cut through some of the outer jacket on the ETA lead to check the wiring, it was in excellent shape. I replaced the Idle speed switch, with no change. I have a spare e-gas module that i swapped but no change there either. I suspect the ETA is the problem. Can anyone tell me what it does on start-up, I dont think it sounds right but im not sure of what im listening to. Or if anyone has any information on testing / reading out the ETA with a multimeter. Any help is greatly appreciated
 

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1977 W123.123 1993 W124.034
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3,829 Posts
That code could be the neutral safety switch. Any record of it being changed? That code also has a number of other possible faults which to get a full diagnosis requires the STAR system. Do you know anyone who has one?
 

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92 400E, 03 ml350, 1994 E420
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21 Posts
Discussion Starter #3
I don't have any access to a star system, so I am stuck looking at the 14 possibilities listed but can eliminate 4 for the N4/1 as well as the harness and throttle position switch. I was trying to read the resistance of the safety switches in the ETA and its potentiometer to confirm their operation. I can read through the switches and confirm their operation when I move the throttle as well as the varying resistance through the pot, but when the key is initially turned I'm wondering about the sound from the throttle. makes me think a gear may be stripped or something bound. I'm going to try to attach a clip. I'll also see if I can access the leads to read out the transmission range switch.
 

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1995 E320 2 Door Coupe 98,000km
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44 Posts
That key "on" ETA whining noise is nothing to worry about. The ECU is talking to the ETA. It's an electromechanical servo system. The ECU is feeding a little bit of locking current into the DC motor while reading the potentiometers. It is simply holding the butterfly valve in position anticipating engine start. It's a good design. On startup the engine jumps to 1200rpm and then slowly drops to 600rpm as things warm up. This is automatic choke for cold start all controlled by the ECU. When my ETA failed, there was a loud horrible squeel coming out of the ETA when I turned the key on. When I started the engine there was no choke feature, it just dropped to 600rpm and ran rough until it warmed up. Then I noticed the cruise control wasn't working. No cruise control is an ETA failure for sure so now it all made sense. I found the ETA schematic and tested the electromagnetic coil. It was burned open. So the squeelling noise was caused by the DC motor running out of control because the ECU can't see a change in the potentiometers. This is because the electromagnetic coil can't energize to grab control of the butterfly valve. I got another ETA from the local junk yard, tested everything with a meter, and checked the harness. I have since repaired the old ETA and now it's a spare. Hope this helps.
 

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1995 E320 2 Door Coupe 98,000km
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44 Posts
K1 looks like the coil indeed. Doesn't show the pin numbers. The true test for that coil is to try the cruise control. Above M1, (labelled as "2") and R1 are the feedback potentiometers for the butterfly valve position. With the key off, you can apply 12 volts to the motor and listen for it. No harm done. S1 and S2 are switches for idle position and full throttle. Everything is easy to test with a meter as you can see. You just need the pin numbers.
 

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92 400E, 03 ml350, 1994 E420
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21 Posts
Discussion Starter #9
Thank you Astronomer
that was just a cut of my page to show the k1 and verify it was the coil (I was not familiar with its symbol), I have the pin #s on the original sheet AES in supplement 14, thank you CBC ATL) so will test pins 10-11 for continuity of the clutch coil. I had already read s1 and s2 and verified their open and closed positions when I moved the throttle as well as seeing a changing resistance at pins 9 and 2 for the pot so im assuming they are fine.
If the coil is open how hard is it to replace, I see that the coil can be purchased on ebay for about $33.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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16,843 Posts
If the coil is toast, just buy a whole unit off eBay that was made 1998 or newer.

I've never seen reman'd/opened throttle bodies last the long haul.

No matter what you decide, you must replace the gasket with a new MB gasket whenever the unit is removed to avoid vacuum leaks.
 

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1995 E320 2 Door Coupe 98,000km
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44 Posts
If the coil is toast, just buy a whole unit off eBay that was made 1998 or newer.

I've never seen reman'd/opened throttle bodies last the long haul.

No matter what you decide, you must replace the gasket with a new MB gasket whenever the unit is removed to avoid vacuum leaks.
I side with sbaert. These ETA's are serviceable only with the right equipment. I bought a newer one at the autowreckers and got the car running again. Then I started to disassemble the old one. What a nightmare that was. The first thing that goes wrong is the shaft coil spring pops loose and it takes some learning to put it back. Then you need to Dremel (grind off) the tack weld that holds the washer onto the main shaft. Then when you're all done replacing the coil, you need to TIG (tack weld) the washer back in place on the shaft. You gotta weld it fast before everything over heats and plastics start to melt. You can send the bad ETA to RestoreyourMercedes.com for repair. There's no cheap alternative. New gasket for sure or you could end up with a mysterious rough idle due to a vacuum leak.
 

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92 400E, 03 ml350, 1994 E420
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21 Posts
Discussion Starter #12
I don't think a 98 or newer unit would do me any good as my 92 uses the pancake style connector.
I pulled the ETA last night (easier than I expected) and I'll get it sent out to either victor or RFC electronics for a rebuild, I ordered the intake boot, crankcase breather hose, and throttle gasket.
Thank you all for your help and advice.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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16,843 Posts
Lots of replacement ETAs were made for these cars starting from the late 90s until even today to deal with the eco junk disaster. They are available without looking too hard.
 
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