Vaden85SEL

Hi everyone,
I just joined this forum because I was running out of ideas from mercedesshop.com. I have found many posts with people experiencing the same problem as I but it seems nobody over there has solved it -- not to mention the threads are almost 4 years old.

Anyway, here is my problem: The 1985 500 SEL starts up and runs fantastically until it gets warm. Once up to temperature, the idle becomes rough and choppy... like it's missing a cylinder or something. It remains choppy for the first few seconds of acceleration and then it smooths right out. As soon as it stops at a light or something, the rough idle and choppiness comes right back. I have changed the plugs, wires, dist. cap, rotor, O2 sensor, and given it a general tune up.

Some posts i have found suggest one of the injectors could be bad, but i just pulled the plugs looking for one that may be fouled and all of them look clean and proper like they are burning fuel correctly. I have also seen suggestions that it may be a vacuum leak, but all of my lines seem to be in order.

This is driving me nuts, and apparently it has driven others nuts too. I am just wondering if anybody may have come across something i missed and perhaps has a more narrow idea of the culprit and how to fix it.

Any help will be greatly appreciated.

Thank you all!

85380SE

I understand your frustrations.... I have a 1985 380SE (which is like your car, only a smaller engine and shorter wheelbase). On MercedesShop, I keep getting the same info as well.

As mentioned, I have a 1985 380SE (with 268K) missing at idle and when initially shifting gears- I have been told it could be a vacuum leak, spark plug wires, "OVP" relay, or fuel pump relay, as well as a host of other items.

I had posted here before about the sudden stalling my 380 sometimes does after the engine is fully warmed after I place it in gear or stop at a traffic light. I have been told it could be the idle control valve.... checked that and it is fine. Idle goes up when it is disconnected. I have not yet tried to check for vacuum leaks, as mentioned here and recommended to me by some here. I was told to start the engine and spray brake cleaner around (on cold engine) to check for leaks. I was told by a local MB indy repair shop that it may be a vac leak and how to check it (by spraying the brake cleaner around the cold engine), but I have not yet checked.

Oddly, the engine has NOT been stalling, but when I first start it of the mornings, it idles smoothly, until about 3 minutes, then it will start "missing", or after I start to accelerate after it has idled, it will start missing/spluttering. There was one occasion where it was like it was "choking" and putting out gassy smelling smoke (black) from the exhaust. Its like it was getting too much gas, but that was only when I placed it in gear instantly and did not let it "warm up" at all. If I hold the accelerator steady when in park, it misses, or even idling, but upon acceleration, or even in gear at steady acceleration, it smooths out. It will do this now until the engine almost completely warms up, but recently, it is missing more often (even with engine fully warmed), if the engine is idling in park, or when it will first upshift into the next gear- then it will smooth out again. BTW - when starting- it ALWAYS starts very easily and quickly... no matter the temperature. In fact the first start of the day is even quicker than the rest of the day- which is still almost instant. Also- it will miss a little when it is idling in park or neutral, but when I shift it into gear, its smooth as silk - when idling in gear.

It did this slightly last winter, but only if the temperature dropped below 40°. During the summer it did not do it, but it was doing the stalling. Now the stalling is gone, but it is running very poorly when the engine is cold if the temperature drops below 60°. It has been getting a little worse every week. I have a feeling it is only going to get worse and worse.

I was also thinking possibly plug wires. I have already replaced the spark plugs last summer, when it was only a minor issue. That did not seem to help and whatever is causing the miss when in park, or when the gears first change is getting worse. Also, I on the highway upgrade that I have to drive up every morning when I leave, I have to take the engine up to 3000 rpms to gain speed. It seems like there is a point when it hits 3000 rpms ( I think in 2nd or 3rd gear - I will check), for a moment, its like something is holding it back.... like an A/C compressor has kicked in (but my A/C belt is removed. I go ahead and let it shift into the next gear and it will miss for about 2 seconds, them smooth out again. The car has 268K, so I know its getting worn out, but when it was running smoothly, I had sufficent power and had more confidence in it.... now I am not very confident, even though it has never left me setting stranded. YET. Also, I have a bad thermostat.... that may be causing some of the problems? On the highway, it drops to about 55°-60C (engine) when the outside temperature is below 50°F. However, in town it goes back up slightly and if I let it set and idle in gear (for an extended period- say, 10 minutes) it will go up to 110°C. My auxillary fan is on the fritz (blows fuses), so thats no surprise. But you would think that in the winter (when it was below 50°f that evening), that it would not go near 110°C.

I guess next on my list when the weather breaks, is to check again for vacuum leaks, clean the coil wires, and replace/check the relays recommended that I check.

I do not want to put alot of $ into this car, as it has nearly 270K and is getting worn out.

Good luck to you!

C32AMG/02

The problem in diagnosing this type of drive ability problem in early vehicles/pre OBD2 is the lack of useful fault codes. If you what to do it your self, you will need some basic tools, fuel pressure and compression gauge, a KV tester or oscilloscope to check for correct spark firing voltage, a vacuum gauge, a vacuum pump or a smoke machine to track down vacuum leaks and the most important tool, shop manuals.


You can start with the basics common cause, Fuel filter and fuel pressure accumulator, located under the passenger side rear of the car next to the fuel pump. Tools needed a line wrench to loosen the fuel line without rounding the fitting nuts. Have it done by a professional; it will be less expensive, less aggravation in the long run. Good luck.

Frankvespe

My rotor under the distributor cap burnt out 2 weeks ago and it was replaced by my mechanic but now the tach is all over the place; I must keep the tach at 1000 or it stalls out...perhaps it is the 87 octane I'm using or maybe the mechanic crossed/miss connected the spark plug cables???? 500 sel 1985, only 129k

Nick Danger

One thing you could check is the Overload Protection Relay in the fuse box. Big silver thing about an inch square and a couple of inches tall. I have an '85 380SE and when I bought it I had a small handful of little complaints. It idled nice on start up but crapped out big time as soon as you put a load on it. That smoothed out when it warmed up. It felt reluctant to gear down, and was just generally sluggish. I really thought is was a fuel problem, everybody on here kept pointing me at the warm up regulator. My mechanic went straight to the fuse box and checked the date stamp on the overload relay and it was original material. He said it was a good idea to replace those units periodically as just about every little sensor and adjuster on the car flows through it. He put a new one in and it was like driving a new car. All my complaints evaporated, it was more responsive and peppier, even got better gas mileage.

Frankvespe

Hi Nick, thanks for the tip, but been there, done that, changed everything in the fuse box...only thing that worked was the idle control valve, $43.00 on ebay...yayyyyy#

Nick Danger

Have you ever done any suspension work on your MB? I'm getting some creaks and groans out of my front end now and then, usually driving over curbs and speedbumps and such. I asked my mechanic to give it a lube and he told me there are no grease nipples on the vehicle, everything is either sealed or uses rubber bushings. (learned something new there ) I'm going back in today and he's going to spray the bushings with a silicone product of some sort. My question here is that if the spray approach doesn't work, are these rubber parts easily replaceable? I've had a couple of other problems since I bought the car that related to aging rubber parts, specifically exhaust system straps and motor mounts, so I'm a little anxious over what the condition of these suspension parts might be. The car is in wonderful shape otherwise, when my brother bought it it had been garaged for over ten years as the owner at that time was getting too old to drive. It's only got about 95,000 Kilometers (60,000 miles) on it so it should have plenty of life left in it.

Frankvespe

Hi Nick-
Are you the same as you were 30 years ago? Nor is our 30 year old Benzs', so I accept the creaks now and then, especially in the front end, but a local mechanic will install upper and lower rocker arms for $100 when I buy them at Advanced Auto parts or another supplier, easy stuff.
I sadly though drive my automatic like a stick, throwing it into Neutral when I come to a light, usually only in the first ten minutes of driving, but now and then it stalls out; perhaps I shouldn't use Regular Gas, a real No-No my friends yell at me, only use high-test gas.

Nick Danger

So if I choose to replace the parts it's not an expensive fix. That's good news. The motor mounts were probably the biggest expense I've incurred so far, aside from a couple of sets of new tires.

Frankvespe

I found fixing my Benz is really not much more than my Hondas, as long as you have a mechanic who is fair and doesnt charge you champagne prices for a case of beer priced car, even though it's a Benz..(i buy the parts)..the local Benz dealer shop told me the car needed $10,000 worth of repairs 2 years ago and it still runs great...I paid $500 for it.

Nick Danger

Too true. I have a guy who specializes in imports as they are a passion of his, and his experience has saved me mmoney on more than a few occasions. We got the car up on the hoist this morning and he found that the boot around one of the lower ball joints had deteriorated pretty badly, more old rubber. He loaded it up with grease and we'll see how long it takes to come back before we decide whether or not to replace it. It's one of those things with a cheap part that takes three hours to change. If it stays quiet then it might be something that just needs a grease job when I'm swapping seasonal tires.

Frankvespe

If it's on the lift and you trust your mechanic friend, throw him a c note and buy the rocker arms and make it like new.

GLENN S.

[QUOTE=Vaden85SEL;1965532]Hi everyone,
I just joined this forum because I was running out of ideas from mercedesshop.com. I have found many posts with people experiencing the same problem as I but it seems nobody over there has solved it -- not to mention the threads are almost 4 years old.

Anyway, here is my problem: The 1985 500 SEL starts up and runs fantastically until it gets warm. Once up to temperature, the idle becomes rough and choppy... like it's missing a cylinder or something. It remains choppy for the first few seconds of acceleration and then it smooths right out. As soon as it stops at a light or something, the rough idle and choppiness comes right back. I have changed the plugs, wires, dist. cap, rotor, O2 sensor, and given it a general tune up.



Some posts i have found suggest one of the injectors could be bad, but i just pulled the plugs looking for one that may be fouled and all of them look clean and proper like they are burning fuel correctly. I have also seen suggestions that it may be a vacuum leak, but all of my lines seem to be in order.

This is driving me nuts, and apparently it has driven others nuts too. I am just wondering if anybody may have come across something i missed and perhaps has a more narrow idea of the culprit and how to fix it.

Any help will be greatly appreciated.


Get a can of brake cleaner and carefully spray different parts of the intake and boots. If you find a leak,mentioned will flare up.

GLENN S.

Also I believe the abs light will be on and the engine will idle fast if the relay goes out.

Nick Danger

That wasn't going on with mine. I was convinced it was a fuel problem until the mechanic suggested changing the relay. There were no indicators lit on the dash, I just got used to letting it warm up for a few minutes before I drove. But I tell ya, the improvement from replacing that one part was incredible.

GLENN S.

Yes, whenever a car comes in the shop with abs light on & fast idle, the relay is bad. It supplies voltage to the idle/ frequency valve management

Frankvespe

[QUOTE=GLENN S.;6802004]