Would really appreciate any help with the problem of the very rough idle on
my 1991 - 190E 2.6, It does not do it all of the time. It starts the very
rough idle only at a stop
light or as I should say a real low idle of 500 RPM or less. I can give it a
little gas and the spitting and sputtering gets worse till it reaches about
800 - 1000RPM, and then its smooth as silk. As I say it only does this maybe
once a week or so. I was told by the Mercedes Specialist to run some Marvels
Mystery Oil in the gas tank, but it does not seem to help. They say it is a
injector that is stopping up, not spraying the fuel right. I have done this
with several fill ups. I have used 4 oz. of this per 10 gal. of fuel. Could
it be water in the gas? I have also used other additives, Injector cleaners,
Heet, Etc. Please Help. Ken
Ken, join the club. I've had the identical problem for a while now and tried
numerous things all to no avail so far. Suggestions for the cause have
- the OVP relay. Not so.
- ICV, Not so.
- vacuum leaks. Not so, judging by spraying Butane over engine without a change
in it's idling character.
- incorrect idle RPM (ie it's 'supposed to be 7-800 rpm). Not so. A 500 rpm
is perfectly normal when under load (D) if nice and steady.
- rotor and distributor cap. the former was good and the latter was a bit
chewed up at the points, but - give me a break - it's a kV spark jumping
- wires. Apparently not, moved them away from engine with no difference in
- I noticed that maybe, just maybe, it gets a bit worse on foggy days and a bit
better on cold and dry days.... could be a clue.
- My best guess is old age and a whole bunch of things are not perfect and
add up to a 'sometimes' rough idle. In addition mine sometimes refuses
to accelerate. If I ease of the pedal and apply it gently it then seems
OK. Then almost like a switch 'clicking' in the car will drive perfectly
after acting up in this manner.... go figure.
cheers and good luck, keep us posted re what you discover
I would check a couple of things.
1. Spark plugs to see if it is clean or you got some odd symptoms.
2. Resistance of each spark plug wires... They should all be below 1300
3. Distributor cap and rotor... make sure they are clean, not cracked and if
you see black oxidation, use sandpaper to clean them off both items.
4. Vacuum leaks. Check every connections... Clear hose to the rubber boots.
Make sure they are tight and grabs. If not, trim the rubber boot back a bit
more to new portions and reinsert clear tube. Test all connections by
spraying carburator cleaner on it... if engine acts different, then you
still got leak.
5. Spray carb cleaner on intake manifold to see if it is affecting engine.
6. Check EGR... be careful as it can be very hot around there...Do this when
engine is cold. There should be a hole on the bottom where you can push up
the internal diaphragm... Start engine... and push up the diaphragm... if
engine stalls or runs very rough, it works.
What mileage do you have on the car now? Most people don't realize that
timing chain need to be changed when you got high mileage... because it
stretches and change the timing. You can try to compensate for this by
changing your timing a little less... for example, if it is supposed to be 5
BTDC, you can go lower to 2 or 0. But other than this, you really need to
change timing chain if engine has more than 150,000 miles. Most mechanic
suggest you change at about 100 to 120K to be on safe side.
Timing chain also affect emission too.
The car is showing about 85K, this is one reason I purchased the car, seemed
like low milage, of course who knows because I just bought it last summer. I
am sure it has been through several owners. The car just started this about
2 months ago. by the way the spark plugs were changed out about 4 months
ago. Thanks so much Ken
I do want to add that the motor surges at a slow pace up and down when this
rough idle is going on. When at its slow idle is when this is going on, but
when it surges to a little faster idle, its smoothes out, and then starts
going down to a slower rough idle. and this is just a repetitious mode for a
few minutes. and sometimes the engine dies. And then for some odd reason, it
starts running like a dream. I hope I am explaning this were you all can
understand this and I am not sounding too nuts. Thanks Ken
Really, I was not the one who figured it out, because I had to get it towed
to the garage. I ask all along, if the Dist. cap and rotor could be the
problem, and the garage said a MB cap and rotor are hardly ever the problem,
they said they are built so tough. Like you said Tiger, the cap was a mess
of moisture, looked like a film of oil, and carbon. I'm sure it was shorting
out. Tiger, I noticed one
of your suggestions was to check this, guess I waited too late, before it
got me stranded on the highway. Thanks for all who responded. Ken
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