Main engine wiring harness rebuild

Mercedes throttle body repair. LIMP MODE ISSUES

Throttle actuator removal and installation procedure on V8

Throttle actuator removal and installation on 6 cylinder cars

A/C evaporator replacement

W220 door lock and close assist pump repair

w140 Bose amplifier rebuild

W140 S class door close assist pump adjustment

W140 door lock pump motor replacement

W163 ML class repairs and upgrades


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Many owners of 1992 to 1995 Mercedes Benz have problems with throttle bodies, also known as electronic throttle actuator or ETA. Almost all ETAs problems caused by shorting wiring inside ETA loom. When ETA fails car goes into so called “ Limp Mode”. On this page you find common symptoms of faulty ETA and explanation of my repair service.

ASR (acceleration slip regulation aka traction control) equipped vehicles enter into Limp mode with ASR and in some cases ABS warning lights illuminate on the dash. Symptoms: no acceleration when depressing gas pedal until half way down, no power at acceleration, RPMs raise and lower chaotically, idle is higher than normal, ABS and ASR warning light are on (ASR equipped cars), cruise control either doesn’t work at all or doesn’t keep preset speed or disengages. Transmission shifts at higher RPMs unless you let go off the gas. Throttle linkage is connected to kick down valve in the transmission and keeps it in gear while gas pedal is depressed.

Cars that are not equipped with ASR option, like E320, E420, S320 have very slightly different symptoms-engine accelerates more or less normal, idle is higher than normal and can raise and lower by itself, cruise control doesn’t work, ABS light can illuminate on dash in some cases.

In both ASR and non-ASR cars transmission engages harsh due to higher than normal idle speed.

Some very few throttle bodies, about 1%, are not repairable due to wear and have to be replaced. But most have failing wiring insulation and wires short out. Those can be repaired replacing deteriorated wires with new ones. In some cases shorting wires burn E-gas computer that will need to be replaced after rewired ETA installed back into the car. It is suggested not to drive the car with failing ETA due to risk of burning E-gas module that controls ETA and cruise control.

First ETA rewire I did was my 1992 500SEL W140. Original wires didn’t show severe shorts but they had lots of cracks in insulation, car went into Limp Mode from time to time. Back then (around 2006 or so) Mercedes used to sell replacement wiring pig tale for throttle actuator. It was available for pancake style flat plug with turn lock found on 92 and 93 model years. Dealers do not sell that replacement part anymore. There was never replacement wiring harness available for barrel type connector with orange O-ring found in some late 93, 94, and 95 models.

It took some time to remove throttle actuator. On the bottom of this page you will find few videos where I talk about my experience with removal and installation of ETA into 94 SL500. There are two vacuum hoses that need to be replaced along with actuator to intake gasket. 6 cylinder motors are slightly different. ETA sits under intake on drivers side. V12 motors have two ETA: primary with linkage on driver side and secondary without linkage on passenger side. And V8 motors have ETA in the center of the motor between intake, right under mass air flow meter. And there is no need to remove intake on either motors. On V8 motor space is very limited but there is a way to work ETA out.

On 96-up V8 and V12 vehicles ETAs are different. They don’t have pigtails anymore and main harness plug in directly into ETA. These newer ETAs fail due to internal plastic gears failures and need to be replaced.

E-class and C-class vehicles used pigtail ETA until 97. These ETAs are known to have biodegradable insulation on wiring that crack and fall off.

All rewiring I offer now are done with military grade Teflon coated wiring. Plastic expandable sleeve is used to run wires in. Plug is cut open, each terminal removed, and new wires soldered directly to them. I also reuse OEM plastic bushing/seal that wires fed through on ETA housing. Silicone is used to seal case cover, plug, and bushing at wiring point of entry. Some grease is applied to gears for lubrication while covers are off. Potentiometer case opened and graphite wear and tear residue cleaned with electronics spray cleaner. Plug is glued together with high strength epoxy. On videos I used heat resistant cloth tape. To create cleaner look plastic expandable sleeve is used from now on. And some original loom and case bushing is saved to create better case seal. Please see some pictures on the bottom of the page for updated look.

All repaired ETAs are bench tested and link to test video is emailed to customer before mailing unit back.

If you experience problems with your throttle body contact me and I will be able to repair your ETA. New ETAs cost $1200-$2400 each at the dealer. And it doesn’t make sense to buy used ones as they use same biodegradable wiring insulation that can fail pretty fast. Even if ETA worked fine in the car it came from, wiring fails during ETA removal as loom gets bent and twisted a lot during removal. I have lots of customers who lost money buying used ETAs that failed either right away or after some sort time after and had their original ETAs mailed to me for rewire.

Some small percentage of ETAs, about 5%, have internal parts failures. I have repaired motor brushes, electromagnetic clutch coils, replaced potentiometer metal sliders. These parts are examined during ETA disassembly and bench test prior to rewire and customer is informed on any issues with internals.

As of 2014 repair prices are below. There is 3% processing fee for PayPal or Credit Card payments. No fee for checks or money orders.

93-95 ETA rewire- $340 plus shipping. 99% of ETAs need rewire only

Clutch coil or motor repair on ASR models, S500, S420, E320, S320-$120

Clutch coil repair on non-ASR units, E420, S320- $200. Grinding and welding required to access clutch coil on these models.

Clutch coil repair on V12 ETA- never saw one fail but based on ETA design coil removal is difficult.

Motor repair on V12 ETA- $200. Due to design flaw all motor issues happen in 1994-1995 V12 units. Mostly when brushes get stuck in their holders due to graphite dust accumulation and motor stops spinning.

Here are some videos of repairs that include clutch coil problem and motor issues:

Mercedes throttle body, ETA, repair ASR and Non- ASR units. LIMP MODE issues

There are lots of bench test videos for my customers on YouTube.

Below is a link to my channel:


Scroll down to see pictures of bad ETA wiring insulation and four videos of ETA removal, installation, and testing in local 1995 Mercedes SL500 I did last year.

You can check the condition of your ETA wiring insulation by cutting outer insulation loom without removing ETA out the car. Or, if ETA is already removed, you can open cover on wire side and inspect wires under cover. If there are signs of insulation cracking or missing, just like on pictures below, ETA needs to be rewired before it burns E-gas module.

Feel free to contact me with any questions regarding repair process and before mailing your ETA over. We go over your symptoms, car make and model, and some shipping details.

Best regards,