Standamac

I start the engine and the idle goes to 10 then drops down to almost 0 and it seems like it is going to shut off. It has shut off a couple of times but not often. Once it the idle drops once its good and it stayed idled at 10 now it's going back and forward from 10-9 so it's not noticeable unless you are looking for it. Once I drive it the idle level out and stay at 10. This happens at every start up. Even if I just shut it off and started the engine again. Doesn't matter if the engine is cold or warm. Please Help.

Lars Nyvold

i had the same problem on my 300e. It,s most likely a fault in the OVP relay (situated behind the battery compartment) I live in Norway (probably the most expensive country in the world,speciallially when it comes to cars & spareparts etc. .a new OVP relay costs approx 4500NOK (950USD) anyway i,ve got hold of the schematics of the relay,and it was quite simple :a few semiconductors,resistors and diodes: This components are (ofcourse)machine soldered,and because the weight of some of the components,they tend to "crack" in the soldering,due to vibrations,age and so on. I used a flat screwdriver to open its metalcasing,and resoldered every soldering just to make sure (15min. work with soldering)then it was just to slide it back into its casing and reconnect it. Car runs like new! (i forgot to mention that (depending of model) but in 99% w124,s no matter what engine (exept diesel ofcourse!) the OVP controls a variety of important stuff,like:Cold start injector,Idling adjustment"motor",Kick-down, and more. It,s not any idea to by a second hand one to save money,since it,s likely to have the same problem (craked/loose solderings). Total time spent:1,5 hour from disconnecting the batteri to gain access to the ovp relay :open it,s casing,soldering,put it back in reverse order. "Piece of cake" type of job. P.S the fuel consumption was drastically reduced to! Good Luck! regards from Lars,Norway

Standamac

Hey thanks a lot I will give it a try this weekend. Did you have any pictures of the OVP's exact location?

Standamac

Hey I went to the salvage yard and found the ovp relay. It was red not blue and it has two 10 fuses not just the 15 fuse like the old one I replace. I started it and it ran fine but I am afraid it might cause problems so does it matter or are they interchangeable?

Lars Nyvold

Hi!
Well to make an swift and short answer:No,i should not cause any problems (i guess you worrying about ECU,s ,etc.)
This relay(s) are certainly not a piece of sophistcatet hardware,and even if they certainly can cause problems,in the end they do what they are inteded to do:Protect sensitive equipment (ECU..!) from sudden spikes i voltage/current.
So i cheked this out there is 2 manufacturers of these relays :SIEMENS and BOSCH and yes!they are interchangable,dont worry about colour,1 or 2 fuses on the top of the ovp (it,s just a different layout from the different manufacturers) But, be aware as i earlier mentioned:If problems occurs: Check the solderings (can be difficult to see these small cracks in factory soldering,so i recommend you to resolder them all,if problem occurs in the future. Best regards.
Lars,NORWAY

Corieltauvus

I have twice had the same problem.
Once on a 180e and today on my 260e (1989) On both occasions the ABS light has also lit up and stayed on. The Over Voltage Protection relay was the problem both times. This relay is situated behind a "floppy" black plastic screen behind the battery (R H Drive). The relay itself is an aluminium cased unit about 25 x 28 mm, say 65 mm high and is covered by a loose black plastic cover that just lifts off. There is a trick to freeing it from its mount. Tilt it forward (about a 30° twist) and its rear arm frees and it can be lifted away.
This relay can sometimes be repaired by a simple re-soldering job because over the years the solder connecting the components to the printed wiring circuit board break away and break connection.
Open the case (you can be quite rough) by easing the aluminium case away all round and pulling the innards out. You may have to lever the bottom of the relay down with a screw driver. Once removed use a hot soldering iron to re-melt the solder at each connection. I then gave mine a short WD40 burst in case the solenoid was a bit sticky.
Worked like a dream on two cars ... note that I am purely amateur ... no great soldering or electrical skills. Just be careful not to let solder short across two tracks on the board. Cost of a replacement part part saved on each occasion!

matthewlexjames

hello i have owned my w124 300e (m103) for a little more then a year now. When i first start the car the idle starts out high and then drops low. It usually ends up idling at 500 rpm after warming up the car for a couple of minutes. Then it starts to jump from there up to 1000, sometimes it drops really low and the car acts like its going to stall or it stalls. This problem started after the car wouldn't start and I found the 10 amp fuse busted on the ovp, ever since then the car has been running really off. I drove it off and on and after awhile the car wouldn't start at all. I replaced the fuel pump relay and the car started again, doing the same thing. The car will idle really low and die out on stops. I think my check engine light was on. At first I thought it was the srs light but when changing out the cluster gauges I found that someone put the lights back in wrong and switch the check engine light and the srs light. Either way the car is not idling right. Ive put in two ovps from the junkyard and it still does the same thing. Should i buy a brand new ovp relay? My car is has a 7 pin ovp and the only new ones i can find is a 9 pin. From what I have seen most of the people with ovp problems have the same symptoms as me.
Thank you.

stormtigers

The OVP guys is renowned for giving problems, some of which don't even seem related such as ABS light on when there is nothing wrong with the ABS.

It is actually wise to replace the single fuse OVP with a two fuse version. The single fuse version can develop issue with solder joins etc as it ages.

OVP Location and How to can be seen here.http://www.benzworld.org/forums/w124...ml#post5087986


Matthew you will probably find that several of the pins are actually blank anyway (i.e not carrying signal).

matthewlexjames

Thank you for the information! I Have order a brand new ovp relay and it will be here tomorrow i will let you know how it goes.