Hello, I was wondering if anybody can help me with a problem I have. I have a 1995 S420 Benz wich has an acceleration problem. While driving down the street one day i lost acceleration and the Check engine light never came on. I took the vehicle to the dealership and was told that the car needed a tune up and a new engine wiring harness at the sum of $2500.00! So I paid the $138.00 inspection fee and decided to repaire it myself. First I replaced the spark plugs, distributor caps, ignition rotors and ignition wires using OEM parts. Still had the same problem. I ordered the wiring harness form the dealer and installed it to have the same problem. The Cap and rotors were worn out and the wiring in the harness was cracked. After I picked it up from the dealer the Check engine light was on. The car has no acceleration and the exhaust smells funny (Running rich maybe?). I dont have a scanner for this car, any help would be appreciated.

 

At this point in the game you should have the car scanned again. I guess code for Idle switch will be present as they are most of the time but the problem you got might not be resolved with that, open up (cut) the wiring harness leading to the throttle, you most likely will find the same scenario as in the eng. harness. Use a razor wire and make a 3-6" incision

Dan

 

This sounds alot like whats going on with my 87 420SEL. Its always running rich, but I thought that was because the guy I bought it from didn't have the right gas cap on it. Also, my car starts to drive as soon as you put it in gear and let off the break. Still don't know what to do, but could this be the reason why its running rich, or because I have a bad throttle sensor?

 

read your post and wanted to know if you found solution to problem
experiencing same issues with a 1995 s 420 54000miles runs rich and idles rough no power on acceleration any solutions let me know thanks
ps no check engine light

 

Sorry I havent been able to respond or thank anybody for their advise but I was having trouble with my password on this site. Heres whats been happening with my problem. I did expose the wiring to the throttle actuator and found it aslo to be cracked. I found someone who rebuilds them in Arkensas and shipped it out, after about a week I recived a rebuilt unit and installed it (Fun!). When i started the car the ASR light was on so I disconected the battery and waited a few minutes. Then restarted the car and drove it around the block, SAME PROBLEM!!!!! This time the Check Engine light came on so once again I take the vehicle back to the dealer to get rescaned. They told me I needed to replace the Ignition wires, Throttle switch (on accelerator pedal) and ASR switch (on dash) for $1200.00. Once again I paid the inspection fee and replaced all three items myself. After replacing the items i drove it and...............Yup SAME PROBLEM!!!!!!! Once again the Check Engine light is on I still have the same problem!

 

hello fellow benz s420 owners I have a 1995 and first discovered there was an engine wiring harness problem last year when the s420 would not start I had it towed to a local mechanic. The mechanic checked out the problem and made a repair using tape then told ne about the wiring harness needing replacing. The fix got me driving the car again. So I removed the air cleaner to expose the harness and it was cracking and bare throughout the ength of the harness. I used lengths of tape for a quick fix. I did some research before I bought another one and replaced it myself. I found out that during that time frame several models of Mercedes had the wiring harness problem which means everyone needs one and there wont be any used ones found for sale. The new harness corrected a few of the sensor problems that caused my temperature gauge to give incorrect temperature and the auxiliary fans to come on.
A few times my ASR light came on and I had no acceleration, I discovered two things I could do 1 was to stop the car and turn off the motor and restart the motor and the car would run normal or 2 stop the motor and in the front fuse box engine compartment pull out each fuse and put it back in seemed to reset something. The car would run normal after that.
Ive got over 232,000 miles on the s420.
I have problems with my door and trunk lock no longer works using the Ir device. yet I can see the light blink.
gas mileage has decreased over the years. now I get approximately 15 mpg and maybe with the new engine wiring harness the mpg will increase. I installed the harness on may 22, the engine runs quieter now. From start to finish the replacement took about 3 to 4 hours.

 

I finnaly figured it out!!!!!!! I was reading a reply to someone elses problem and read that someone had the same problem as me and the key thing was that they said the exhaust smelled funny! It doesnt smell like its running rich, it smells like bad gas or just plain funny. It ende up being a Coil!!!!!! I replaced both and now the car runs like new! (It should since I replaced pretty much everything trying to figure out this problem!) I hope my problem and solution will someday help someone else, Thank You to everyone for your ideas and information.

 

I have a 1995 mercedes s420 which suffered a misfire and I changed the distributor caps, rotot arms, and plug leads. That cured the misfire but I noticed a strong smell of petrol, low mpg and very bad acceleration from a standing start. The local main dealer suggested new plugs which have been done. It is still the same. It is the 119971 engine which idles alright in park but misbehaves under load. A specialist thinks it might be the exhaust. any ideas not as expensive as this..

 

I have had the car scanned again by a main dealer and they have diagnosed faulty coils. These have damaged the recently replaced distributor caps and they further suggest that I relace the ignition leads that I bought on ebay as they are poor quality. I will carry out this work tomorrow and report on findings. I hope it cures the poor mpg and fluffy acceleration. The wiring harness also looks bad but is not causing a problem at present.