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  #1  
Old 10-29-2001, 10:18 PM
olivo880
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1986 300E - 3n ew problems after service

I recently had my car serviced because it began stalling at idle (cold, warm, & hot). It was serviced at an exclusive mercedes shop in Orlando that had serviced this car for the last 5 years for the previous owner. They fixed the stalling problem (motor vac, fuel injectors & seals and coolant temperature sensor, distributor cap, rotor, plugs). To me it seemed like the shotgun approach, but, I'm no expert. They also checked, coil, fuel pump, fuel distrbutor, o2 sensor (at one time they said the 02 sensor was bad, but, when I complained about how could so many things go bad at once, they said they cleaned it and it tested ok) $1,200 Total.

Anyhow, when I left the shop, my car had 3 new problems. First was obvious - LONG CRANKING (3-5 sec) cold, warm or hot. Previous to this I could crank the car in 1- 1.5 seconds. I mentioned this to the shop owner, and he said he owned the same car and 4-5 seconds of cranking is normal for this car. Wrong answer. I found a workaround by holding the gas pedal down while cranking. This helps crank in 1-1.5 like before.

However, after I start my car, comes problem number #2 VERY ROUGH IDLE. The car will cough and gasp for several minutes. Occasionaly it may die and I will have to re-crank and lwait for the car to warm up before moving. But, what is odd is that this happens after cold and warm starts but gennerally not hot starts. Mentioned this to shop owner and he said this is most likely the resistor ends. For a fee, he could look at this and replace and bad ends. My only work around to this is to keep the RPM's above 1K until the engine smooths out.

Now before you comment let's go on to new problem #3. When coming to a medium to quick stop, something in my (and I think it's either the engine or transmission) VIBRATES and makes the car SHUDDER while stopping when the engine goes below 1k rpm. It even shakes for several seconds after stopping. The engine sounds like it's about to stall but it does not. This happens predictably. Mentioned this to the shop owner and he said the motor mounts were collapsed. Now here is an interesting observation, if I shift to neutral before braking, I can brake as hard and quick as I want with ABSOLUTELY NO idle roughness whatsoever. Behaves just like you would expect a mercedes to behave. I ruled out warped rotors because in neutral while braking problem disappears 100%

Now, I don't mind having the motor mounts, resistor ends and/or wires replaced, but, I wanted to get some expert opinions from the masters out here first, because I don't want to go in with 3 problems this time and come out with 9!

In summary I now have long cranking, rough idle (cold & warm), and vibration while/(and after) braking, except if I brake while transmission is in neutral.

What do you think is causing these 3 problems and why didn't I have these problems before I put my car in the shop?
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  #2  
Old 10-30-2001, 04:34 PM
MIKE FREEMAN
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CHECK OR HAVE THE FOLLOWING CHECKED.
FUEL MIXTURE (LAMBDA SHOULD OSCILLATE AT 50/60%)A LEAN MIXTURE WILL CAUSE STALLING AND POOR IDLE.
VACUUM LEAKS. WILL CAUSE THE SAME.
WHAT KIND OF SPARKPLUGS WERE INSTALLED.USE ONLY BOSCH H-9DC AND SET THE GAP AT .036IN.
IF YOUR NOT USING REG. GASOLINE,SWITCH TO REG. NEXT TANK
FOR BETTER STARTS.
IF YOUR ENGINE IS USING OIL IT MAY BE TIME TO REPLACE THE VALVE GUIDES.DECELERATING IN GEAR CAUSES HIGHER MANIFOLD VACUUM AND IF GUIDES ARE WORN MORE OIL WILL GET SUCKED INTO ENGINE AND FOUL PLUGS.
MF
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Old 10-30-2001, 10:55 PM
olivo880
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I forgot to mention the shop said they corrected some vacumm leaks. Spark plugs are H9DC. I tried a tank of 89 octane but saw no noticable improvements so I'm back to 93. My service records indicate the previous owner replaced the valve guides at 145K miles.

1986 300E 199K

Ran like a dream until I had it serviced.
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  #4  
Old 10-31-2001, 12:18 AM
Gilly's Avatar
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
Olivo:
I would really contemplate trying someone else with the problem, unless you can threaten a little with going elsewhere and have the shop owner concede that something is "a-miss" and figure out what happened. By the sound of it, my guess would be a goofed up cap and rotor change. Did/do they use MB or at least aftermarket Bosch products? Possibly 2 of the plug wires were reversed when putting the wires onto the cap, believe it or not they will run like this. OR the center contact in the ignition cap could have been damaged when installing.
I think the shuddering is just being caused by the engine missing when pulling to a stop due to the miss in the engine, more noticeable at lower RPM's. The motor mounts may be wearing out, but no reason to notice that it's worse just because the engine was tuned up.
Another thought is that you can try gently pulling on each plug wire to make sure they are all snapped into place and not loose, this can cause a miss as well. They can't hardly be put onto the wrong plug (on the cap they can, as I mentioned already) but maybe not put on tightly. The torque on the plugs is 20nm, is you want you could doublecheck to make sure the plugs are all fairly tight, a loose plug could also cause a miss. Spark plug gap on all but the latest engines is .032". I recommend the H9DCO plugs, only difference is a heavy duty center electrode, the H9DC is fine though. I forget what year your car is, but in April 1988 the H9DCO became the recommended plug anyways.
Checking the on-off ratio is a good idea, but I would try approaching this from the standpoint that you now have these problems that are new, were they caused by the service work?
Gilly
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