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Discussion Starter #1
I just bought a 1993 300TE with 235,000 miles on it. The car has a new radiator and water pump that were installed before I bought it. I was told that the car never overheated until these parts were installed. The seller was at wit's end and sold me the car at a low price. I suspected an air lock in the cooling system, and after bleeding all the air out, the car does not overheat anymore. It does have the following issues:1) It does not idle at a constant speed, I guess the proper term is 'hunting idle'. It revs up and down all itself. Engine cold or warm it does the same, either way. 2)The electric cooling fans do not come on at anytime unless I unplug the sensor located at the thermostat housing, then they come right on and only shut off if I reconnect the plug. 3) Where the heck did they hide the spark plugs and distributor on this engine? I am used to Fords, Chevys and a Porsche or two, where all that stuff is out in the open. 4) There is a tank on the left side of the engine compartment that says "hydraulic oil" What is is for, and what type of oil do I need? As you guessed, I am new to Mercedes Benz and would appreciate any and all answers to my questions. I think this is an interesting car and I'd like to get some use out of it. Thanks.
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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4) Its for the self leveling suspension (SLS). Its a great system if it works. It needs special MB or Febi Self Leveling Fluid. Not not use anything else.

Make sure you are using MB coolant or Zerex-G05. You may also consider getting a new thermostat.

The electric fans should come on with A/C pressures, or when the coolant temperature hits 107C I believe is the trigger point. Unless your ambient temperature whenever you live is above 95F, you shouldn't be getting anywhere near that mark.
 

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95 E300, 91 300TE, 84 190D
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Factory Service Manual

3) and almost any other repair issue, up in the 124 DIY Thread sticky are two options for accessing the FSM online for free.

It will teach you about your 104 engine and how to get the black cover off the valve cover to reveal the spark plugs and three coil packs.
 

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1995 E320
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There is no distributor. The engine has 3 coils in a coil on plug set up, where each coil fires two cylinders; 1& 6, 2& 5, and 3&4. Coils are located directly above the even numbered cylinders.

Spark plugs are hidden beneath the panel on top of the engine.

Loosen connecting wire to MAF sensor. Set aside.
Loosen clips at MAF sensor.
Remove MAF. Set aside.
Remove 10mm bolts holding crossover pipe to top of engine.
Loosen hose clamp at intake (drivers) side where it connects to the plenum.
Set aside the cross over pipe.
Remove six 5mm allen bolts holding top panel.
Remove panel.

Voila.

Use copper core non resistor plugs. Search to see which ones.
 

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Discussion Starter #7
Well, I have several hours into reading various posts regarding the idle problem I have with my car. I've noticed a tendency to speak in initials and abbreviations here, and that makes it tough on those of us 'not in the know' with these cars. For example, I had a heck of a time finding out what a "OVP" is, but once I did I looked at mine at it appears to be original, in that it has only one fuse on top. I checked voltage with the engine running yesterday and had 13.2. The hunting idle condition persists after cleaning the MAF, fixing any vacuum leaks I found, making sure the grounds are all clean and tight etc. Took it for a drive yesterday and observed the temp gauge climbing, so I turned around and came back. It was pegged within 1/4 mile, BUT the engine and radiator did not feel overheated, nor was the coolant boiling in the recovery tank. Today, I started it up and it did the usual erratic idle for awhile then it settled to an almost acceptable idle with an occasional surge and for about 30 minutes it would vacillate between running ok and surging up and down. All the while the temp gauge was just above the 80 mark as it has been normally. I noticed that the needle would jump up high for a second or two, then come back down to 80, then jump up again. I checked the voltage across the battery again and today it was 18.2 volts. Could the voltage regulator and/or the OVP be the problem? It amazes me from what I have read here the myriad of problems these cars have with the electrical systems and how things one would normally not associate with a particular problem can actually be the cause. I've read about the 'eco-junk' wiring harness which made my hair stand up. Is this what they mean when they said "Engineered like no other car in the world"? Honestly, it has me longing for my 912 to break down so I can have something that is easy to fix...................
 

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86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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By now you may have read what to check for to determine if your upper/lower harness and throttle actuator are original or have been replaced. Let's hope the latter.. The hunting idle problem you're having is strongly associated with the OVP relay. The OVP has a play in all underhood electronics. When they fail, the most common trait is hunting idle. It is a good investment to replace it with an updated model (2, 10 amp blade fuses) . Use only a MB unit or one by KAE(ler). Either of these will be in the $65 neighborhood. All the others you'll find are priced at 1/3 the cost or less and are a waste of your money.

These cars are very sensitive to correct, constant voltage. If you're getting 18+ volts at the battery, your voltage regulator is kaput.. It is an inexpensive item and very simple to change out. The VR is located on the back of the alternator and held in place with 2 phillips screws. Takes about 15 min. to change out. Online units can be had for under $30. NAPA units are about $40. Invest a few dollars in new fuses. Replace every one of them with copper fuses instead of the aluminium ones that are most likely in the car.

Good Luck

Jayare
 

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Discussion Starter #10
So, here we are after the new voltage regulator installation. A Bosch part that took two days to get here. The car runs just as it did before, voltage across the battery is 14 with the engine running. I think I will look into the OVP as it seems that could also be part of the problem. I noticed after running the engine for about ten minutes, the OVP is very warm to the touch. Am I on the right track with this? I don't want to just keep tossing parts at it, but I would like to get it fixed. Can anyone recommend a MB mechanic in the Cleveland Ohio area who will not take advantage of my ignorance?
Thanks for any and all replies.
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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Don't do anything until you replace that OVP. Its such a horrible item to diagnose and its so erratic its pointless working on anything until you rule it off.
 

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Discussion Starter #13
New OVP, same problem. The high point of the day was driving the Porsche to the Mercedes dealership for the part. One of the saleslizards asked me if I was considering "trading up to a Mercedes". I told him no, I was driving the Porsche because the Mercedes doesn't run. Next on the list is to revisit all the grounding points, and if that fails I may consider the possibility of incorporating it into the landscaping.
 

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Discussion Starter #15
This is encouraging. I have replaced wiring harnesses on other cars due to fire/collision damage so I am no stranger to this. I have heard the wring harness is around $1500 from the MB dealer. Is that true? It may be time to cut my losses and re-home this one. I guess I am a little disappointed, having lived my life hearing about the superiority of the Mercedes Benz. To have the problems these cars have would lead one to believe it is a car to run, not walk away from. Now of course I know this is not a brand new car, and I am sure the new ones are great if you trade them in every two years.
My daily driver is a 1964 Ford. In 47 years and 112,000 miles it has had one generator rebuild, one water pump replacement, a brake job or two, and normal wear and tear items. No wiring harness failures, oddball issues, just one of the most reliable and easy to maintain cars I have ever encountered.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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The eco junk wiring issue affected every MB made between MY92-97.

It is one of the biggest fiascos in MBs history, no thanks due to the Euro tree hugger mandates.

Of course, MBs arrogant attitude towards the problem by simply refusing to recall the vehicles and letting the customer foot the repair costs didn't help things either which probably only helped Lexus gain a loyal customer base.

In your case, I would verify the build date on the harness and throttle assembly. If either was made before 1998, then you know the decision you need to make. Based on your mileage, I would venture to say that it is likely the harness has already been replaced but the throttle actuator probably hasn't. A telltale sign of a bad throttle actuator is to check for cruise control operation. IF CC is non-op, then the throttle actuator is the most likely culprit although I have encountered a few exceptions to this rule. In other words, until all of th eco junk wiring has been replaced, these cars are nearly impossible to troubleshoot electrically.

$1500 for a new harness is too high. Shop around on the internet, BUT make sure you get the harness p/n# that is VIN coded to match your vehicle. Actuators are available from autohausaz.com, among others.

Be aware that there are 2 versions of the throttle actuator, depending if your vehicle is equipped with ASR or not. The 2 actuators are NOT interchangeable.

Other than that, these are great cars.
 

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Discussion Starter #17
After cleaning every ground I could find, the car ran as it has been for about ten minutes. It eventually settled into a fairly smooth idle but not perfect. I decided to leave it alone for awhile and see about filling the hydraulic tank that is under the hood. Filled it up, then noticed a huge puddle forming under the rear of the car. It appears to be a leaking line that is hidden by a plastic splash guard, so for the time being I will note that I 'flushed' rather than filled the hydraulic system.
What is "ASR"? Thanks for your help.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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ASR = anti-slip regulation a.k.a. traction control

The fluid leak is most likely coming from the control valve for the self leveling suspension or one of the hydraulic fluid connections for the SLS nearby.

Regarding your idle issue, has the ignition system ever been overhauled as in 3 new coil packs, 3 new spark plug wires (Bosch or Beru), 3 coil to plug boots and 6 solid copper core non-resistor spark plugs??? The entire ignition system is a consumable item requiring replacement at least every 100K, with the plugs needing replacement sooner at 50K intervals.

Still waiting on feedback if your cruise control is functional. If not, the issue is very likely with the throttle assembly..
 

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Discussion Starter #19
Don't know if the cruise works because I have not driven the car long enough to try it. I do not know if the ignition system has been overhauled. If it hasn't, that along with the SLS control valve sounds like it's going to add up to another big pile of money. I'll have to ponder my next step and give serious consideration finding someone willing to devote the time and money to make this car as great as they allegedly are. Thanks again for your reply.
 
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