Riot Nrrrd

My 1989 300E (192,000+ miles) has been running like a clock, but in the last few days it's developed a nasty habit - after driving it for a bit, like for example being on the freeway and then exiting onto surface streets and coming to a stop, it has started randomly shutting itself off (like as if I'd turned the key halfway off) when coming to a stop. Obviously very disconcerting and a serious safety hazard. (I'm amazed no one's plowed into me yet)

It did it once after a 50-odd mile drive to Ontario International Airport last Friday, then once again on Sunday when I returned. But yesterday it did it 4 times on the way home from work, which is too scary. It would restart immediately after turning the key and sometimes it wouldn't do it when coming to a stop, but I can't trust it now.

I am scheduled to take it in on Thursday but thought maybe it's something simple I'm missing. Someone suggested the battery was dying (it's several years old) - but wouldn't I have problems starting it if that were the case? Or if the alternator was having a problem wouldn't that cause random turn-offs rather than just at stop signs/lights? Same thing for loose/flaky distributor issues, I would think.

shdoug

I would clean the idle control valve first. Does it have a rough idle, or just the stalling? A rough idle could be a vacuum leak and that could cause stalling after a coastdown.

YNVDIZW124

It's your fuel pump relay, change it and it should be back to normal.

Riot Nrrrd

shdoug: No rough idle. It's fine until literally the very second it dies. I don't even hear any noise from the fuel pump.

YNVDIZW124: That sounds reasonable; but wouldn't something like that potentially trigger at any time? I find it odd that it (so far) only happens when I come to a stop. Thank goodness it's only at those moments!

YNVDIZW124

You should hear some noises from the fuel pump or else it's not working..

Well when the fuel pump relay goes bad it's pretty intermittent. When mine was bad it would randomly shut off and sometimes at stops it would idle but then die because there was just enough fuel in the lines. Listen to your driver side by your battery and if it makes a buzzin noise then it's your fuel pump relay. Also when the car dies try to wiggle the fuel pump relay and start the car.

Riot Nrrrd

YNVDIZW124: I'm normally used to hearing a fuel pump noise from the back when first starting it, then nothing thereafter. My battery's on the passenger side, is yours a right-hand drive?

Where exactly is the relay to wiggle? The car starts instantly after it 'dies', btw. (So far) I'd love it if wiggling it made it work better until Thursday morning!

I'm wondering if before then I should try shifting into Neutral as I approach a stop light/sign and try and keep it revved while braking.

In the meantime I guess I'll just have to drive the CLK55 instead

Rio Z Lander

my car did this if i ran low grade gas in it. also it did this when my battery was going bad on me. it could be a fuse problem also that turned out to be 70% of my cars problems it could possibly be your OVP fuse thats is going bad

YNVDIZW124

oops yes i meant your passanger side..

It's the one behind the computer and in front of then KLIMA relay by your battery tray. If you put it in neutral and you are able to hold the revs for more than a min then it could be your EHA valve. If you put it into neutral and it just stalls after a while from running out of gas then it's the relay.

These are my spare relays I have like 3 sets just in case...The OVP relay is the one next to it..

GEDaggett

Question, Where is the idle control valve located (94e320) and what needs to be done to clean it?

shdoug

Yours doesn't have one. I believe your idle on the M104 is controlled by the electronic throttle actuator.

GEDaggett

That explains why I couldn't find one. Thanks

ps2cho

That would be your OVP That exact problem plagued my 300TE until we replaced it.

Get right on it! Its about $60 and an easy "plug n play"!

It is located right next to the ECU behind the battery (hidden by a plastic cover). Rectangular box with 2 fuses on the top.

Riot Nrrrd

Update: Car has been in the shop a week and a half now. They still don't have any answers. They even tried a new ignition coil and that didn't solve it. Latest attempt was to replace cracked vacuum hoses(?). I know they aren't spending all day on it but at this rate the labor charges will start to approach the remaining value in the car! Very frustrating

shdoug

Did you replace the OVP and Fuel Pump Relay yet? You could probably do them both for the cost of an hour of labor at the stealership.

GEDaggett

Agreed. sounds like they are just throwing parts at it. You can do that on your own and it will save you a ton of money. Most of those parts you can get at the bone yard and then when you get the part that fixes it nailed down then you go buy the part new. There is a progression to follow in diagnosing a problem that I always use. Replace the cheapest most likely culprit first and then work down the line. This is after you have done all the diagnostics and remain without the cause. This is what the dealership does but they charge you $130 an hour to do it.

YNVDIZW124

I would be really mad right now since they are still charging you. If a mechanic doesn't know how to fix a mercedes they shouldn't charge you to learn how. I had this happen with my first mechanic and he changed all kinds of parts always asking for more money. I would take the car back and read the forums and see if i can fix it myself. Once you know how your car works then it's easier to find out how to fix it.

georgedaman

if you went through the regular OVP relay and the klima box ,It is mostlikely the ECU....The only way to make sure either get a loaner which works for sure (i got a used loaner ECU from MB and guess why they had it....had the same problem.)...or just pull it out and drive the car without it..if it doesn't stop..there is your answer..

Riot Nrrrd

This isn't a dealership, it's an Independent Mercedes place near my work that I've been taking my car to for years and years now. Usually they have things fixed in a day or two. It's perplexing to all of us at this point. As one of the guys told me yesterday, "We've seen other cases of cars dying but not like how yours is doing it - they either stay dead or they can't start it right back up immediately thereafter like you can". The main guy hasn't had it quit on him once, the other guy had it only happen to him once. I get it back, go up around the corner and to a car wash, and after I got it washed and headed off to work, boom - it died at the first stop light I hit. Guess I have the Midas touch?

I drove it home last night and it didn't quit when I got off the freeway, as it usually does. It is very intermittent and thus hard to diagnose. They have already checked the OVP and the fuel relay filter.

I work in software and we have this phrase - "Works in my office". People will come in with problems, I'll remotely log onto their computers and try it, and it will work fine for me - but they swear that it fails for them (and it often does, and right in front of my face). It's like this weird Law of Nature that says when the fix-it person tries it, it won't show the problem

crr1612

if its a stop that it causing it, maybe the fuel delivery is being cut off. is it possible that the fuel cut off switch (when your car flips) accidentally getting tripped?

DarkHand

Have you tried to check the wiring harness?
I had intermittent shutoffs just like yours, silent and deadly.
My problem was deteriotating wiring going to the coils.

If your wiring harness was replaced then this question is moot.

lardog1

If you haven't fixed the problem please post again. The same thing was happening to my 89 300CE while going down the road. It took a while to figure it out but it was a relay in the ABS system. Hope this helps. Dirty contacts or so they told me.

Riot Nrrrd

Update:

Nothing's worked yet.

They've since replaced the OVP and the fuel relay and it still dies on me. And a couple of other things have been tried that haven't worked (but I forget what they were).

I will pass on the suggestions about the deteriorated wiring/wiring harness and the ABS system relay (thanks, DarkHand and lardog1).

Pretty soon we might try disconnecting the ECU but my mechanic warned me that it would make starting the car problematic in cold (it's in the high 40's by the time I leave work, most nights) and I'd have to let it idle a few minutes at operating temperature before setting off, etc. But I'm willing to try almost anything at this point. It's really getting frustrating to me, and baffling to my mechanics.

ps2cho

The wiring harness is not a problem on your year. It was 91 through 96.

Another thing to pass onto your mechanic would be to check your fuel pressure. Your Fuel pressure regulator is another suspect item.

GEDaggett

That switch is often connected to a oil pressure sensor as oil pressure is the first thing to go when your car is on it's head.

Riot Nrrrd

Sorry folks ... slow on the uptake to update the thread ...

And the winner was ... <*drum roll*>

A bad Idle Air Valve.

Was a real head-scratcher for my mechanics ... especially because early on, that was one of the first things they looked at. They even cleaned it off at the time but thought it looked OK. Then we started the cycle of all the other parts that didn't work. Finally in frustration one of my mechanics just decided to disconnect the damn thing just for grins (next step was gonna be disconnecting the ECU), and damned if that didn't make the shutting off stop. We put in a new one and so far so good. Idle is back to normal and doesn't drop below 500-600 rpm.

Can't wait to see what the total bill for this will be ... LMAO