"86 300E Probs...puzzled?

Sounds like overload relay is bad... are you sure your car actually have 30K miles? Have you run carfax on it?

I suspect the "overvoltage protection relay" is the cause.

Yes, I bought the car from a family friend, I am very familiar with it's history.

The Overload Relay is located behind the battery, I assume. There are four components back there, I am not sure which one it might be.

I thank you for your post.

If you got to online parts store... like bimmerparts.com... you can see the picture.

Is the "overvoltage protection relay" the same as the voltage regulator...if it is not where is the "overvoltage relay" located, and were do I get one.

Thanks - Vincent

No, the voltage regulator is inset into the alternator.

The overvoltage protection relay has a fuse on its top, but I can't tell you its location except that it's under the hood.

It is located behind the battery... overload relay has a fuse on the top... other relays that might have a fuse on it is sort of on the side whereas the overload realy is all on the top.

I have an 87 300e and have exactly the same problem as described, however I've already changed the Overvoltage Protection Relay on my car as part of an ongoing effort to sort out a series of problems with the fuel injection system, so far including the OVP, the ECU, fuel pressure regulator and all six injector nozzles.

The ECU was changed because it was corroding inside, the regulator to cure a warm start problem and the injector nozzles because the new pressure regulator caused them to start leaking :)

The problem is intermittent and seems to go away each time I change a component, only to come back after a few days. The idle speed is erratic and now it has started stalling in traffic. While running at low speed it alternates between an apparent misfire and picking up speed on a steady throttle.

I'm about to change the oxygen sensor to see if that works, as I've seen a previous post identifying it as a possible cause of the problem. My mechanic fiddled with it last week and cured the problem temporarily so it's looking a likely culprit. If that doesn't work, it will be the idle control valve next.

If anyone has successfully sorted out this issue, would love to hear how to fix it before i have to blow a fat wad on the fuel distributor because nothing else works. Love the car but this is driving me nuts.

It is rarely the fuel distributor... even if you think it is, have it rebuilt by Bosch authorized repair center. You wen't through alot of replacements without success... I suggest you start basic...

What is your compression readings? What is your cylinder leakage? Do you have tapping (Valve) noise? Have you tried Mobil 1 engine oil? Have you tried putting in Marvel Mystery oil into the engine oil or a little bit in gas tank as directed by their direction?

I had a idling and hesitation problem on my 380SE but I knew it was a valve problem because it has been tapping all its life since I got it... only that it got worse all of the sudden when I used a very heavy concentration of fuel injection cleaner... never a problem before... After doing just a few diagnostic, I knew it had to be valve problem...

So I decided just for the heck of it... try Mobil 1 oil... and a quart of Marvel Mystery oil... to the factory oil level (Never Overfill!). After one block, all the problem disappeared. Valve tappings was LOUD but it gradually came back to normal tapping after a gas tank or so.

Oh by the way, replace your fuse for fuel pump inside your fusebox before you do anything else. The reason I said replace is because by simply looking at it, it will apprear fine... but upon removal, you might find corrosion at the contact spot... or it might simply fall apart when you do so.

MB fuse are notoriously deceptive... it looks fine, but it might not be.

Actually, if you are changing them, change them all to the copper/brass ones, and not the tin-based (silvery) ones. They will turn dark, but are less likely to corrode into white dust unlike the tin-based ones.

Cheers, WS

Well, OK, I use Mobil 1, and my valves are fine...

sure its a fuel system problem because I can see the effects at idle with the air cleaner off. Runs smoothly on idle most of the time then sucks down the throttle disk and speeds up every so often. Before I change the O2 Sensor, I'm going to be looking at the idle control valve and see if there are any leaks in the hoses, as it's sounding more and more likely to be something like that due to the intermittent and random nature of the problem.

I also suspect it could be a bad contact with the ECU (Fuel Pump Relay) and the OVP mounts. I'm also getting some water leakage in there behind the battery when I wash the car so may be a short happening. Both units are new and I gave them a wiggle this morning and engine ran fine all the way to work.

Some questions though: If I can't get new hoses for the ICV, would there be a problem if I used a sealant to ensure there are no leaks?

No need for sealant... new hose will be quite tight fiting.

the gasoline mercedes is fine is you have deep pockets, if not get a diesel, a lot less problems.

It is true that diesel is alot less maintenance than gas... but having gas doesn't mean high $$$...

As a followup to my question about surge/idle problems on my 87 300e, just like to report that the problem appears to have gone after I did the following:

1) changed the potentiometer with a known good secondhand unit 2) replaced the lower vacuum hose attached to the Idle Control valve which was cracked at the join 3) cleaned the ICU with carb cleaner.

Now, although this may be of help to others with the same problem, I should also report that the surge problem wasn't happening on the day I did the changes so there is the renote chance it was due to soemthing entirely different and cured itself

And although the car is generally running great, after its been running for a while, it still occasionally idles unevenly while stationery, although not as drastically as before - 700 to 1200 rpm as opposed to 500 to 2000 rpm.

I suspect this may be due to the ICU sticking and I'm considering trying further cleaning or buying a new unit if this continues to see if that works.

My mechanic at the local Mercedes dealer says this is most likely to be down to incorrect CO settings and these should be adjusted. I plan to run the car for a week or so to make sure its OK as the problem itself was intermittent so could be back.

Hope this helps

It sounds like a computer problem like the black box behind your left kick panel. The mileage on your 124 is unbelieveabley low! Did you run a Carfax on it? I would check the plug wires before anything. That could answer the radical tach action. P.

The speed sensor switch is dying. It's mounted just below the starter and the cable runs all the way up to a place behind the battery. It's part #010-542-22-17, and dealer retail is $59.80. It can be had for $46 from Rusty Cullen at 800-741-5252. You'll need a lift to remove the switch from below the starter. P.

Wrong... my friend got this exact problem... turns out to be the overload relay. Rusty's price is expensive.