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Discussion Starter #1
I have a problem with rough idle when cold. When the car warms up it goes away. I already had MAF swapped and changed few other things.

My uncle suggested this might be an ignition wires problem. His VW Sharan was working rough when cold and it was a bad ignition wire.

Could it be as simple as that?

I don't know when were the wires last changed on the car. I changed only the plugs quite recently.

Is there any way of checking it before I buy all the pieces to replace ignition wires?
 

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How long since the dist. cap and rotor were replaced? Those wear out after a while and get corrosion on the terminals, before the wires wear out. I would chjeck those before replacing wires. But if you do need to replace the wires, Kingsborne in San Diego, CA makes a set I have bought two sets from them about $100 US a set, and was pleased with the quality and fit. Good luck,
 

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Discussion Starter #3
No cap and rotor on my engine. 1993 M104 is a little bit different in terms of ignition.

Also - I am located in Europe, so I'd rather shop locally.

Thanks for input!

Anyway - I'd like to know the symptoms of bad wires.
 

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Usually if your wires have a bad one or more it doesn't change characteristics when it warms up, it might misfire a little more at higher RPM though. Possible vacuum leak? If the problem only recently started, possibly check that the plugs are the ones that esteemed forum member Jayare recommends, and that the gap is correct. You don't want resistor plugs because these cars wires have resistor built into the end of the wires that connects to the spark plug. They say that platinum plugs have a lower intensity spark, however I used them with no bad result. I have since changed my M104 to a Bosch F8DC4 as per Jayare's recommendation and all is well. Many years ago, I changed plugs on a car then shortly after that, it quit running altogether and we spent countless hours and days looking for the problem, can't remember why but it finally was learned that the plugs were the problem! To check the plug wires, use a volt meter and check the resistance of each wire, they should all be very close in terms of resistance. If one or more are very different than the others...voila. Also look closely at the connections at each end making sure there is no corrosion or damage. I always use white silicone grease on the spark plug end to make sure the wire will remove easily without breakage next time, and I always use anti-seize lubricant grease on the spark plug threads. My 1990 M104 has distributor cap, rotor, and single ignition coil which I replaced with a 60,000 Volt Jacobs Electronics Ultra Coil which gives a very powerful spark. But that's just me. Be very gentle and careful when removing the wires (one at a time so you don't get them reinstalled incorrectly) remember that they are expensive and if they are indeed in good order you don't want to break one of them and then have to replace...Good Luck,
 

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How about engine wiring harness upper and lower? You have the dreaded 93-95 year car. Pull back some injector insulation and look. Also coil packs being aged can cause alot of problems.
 

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if your not sure when you changed the wires then i would change them then.
coolant temp sensor. could be telling the cold engine that it is warm, then when it warms up it runs properly.


single ignition coil which I replaced with a 60,000 Volt Jacobs Electronics Ultra Coil which gives a very powerful spark.
how does this work for you.my hotrod has one on it also.
i was thinking of buying one for the benz but did not know if it work.
i find the benz has a low coil output.

did you do anything special to make it work, i thought maybe the coil had something to do with the on board computer.
 

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Mine being a 1990 has a regular coil instead of the coil paks the later ones have, the Jacobs Ultra coil works very well. Just your pos, neg, ground and high voltage lead. I have used this coil on most of my cars now since the 1980s with much success. Also have one on my 1989 190E 2.6 ~ No problems at all with engine's computer. I had a special coil-to-distributor cap wire made for them by Kingsborne in San Diego for under $20.
 

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Discussion Starter #11
I just checked the ignition wires.

A friend of mine reminded me that you can see sparks on bad wires when it's dark.
It's 1 o'clock in here, so I pulled the cover and started the engine. When I found a place where it was really really dark - voila! - discoteque! There were blue sparks under the coils and all around the wires.

I guess they are bad. And I think they are responsible for my rough idle issue.

I will let know what will be the results.
 

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OmiGod! Good work. New wires are going to make a huge improvement. Your power will be smooth and your gas mileage will increase. Congrats. Look around for the best deal on quality new wires. They can be pricey.
 

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Very very interested. I have evidence of arcing as carbon deposits on my coil wire. I too have been chasing a rough idle/2 crank start issue for a couple of months, but haven't thought to check it out "under the stars" as was also recommended to me.
 

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I had a bad spark plug wire in my other car (Acura LS) once. The car idled fine but it could mis-fire at higher RPM occasionally. It was my fault. I shouldn't buy generic brand wire from Pep boys. After I replaced the wire with NGK, problem went away.
 

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Ya well the computer is losing its mind trying to make it fire if those coils are bad so dont wait to long. Just so you know lots of people have a habit on Benz' not changing them for the same reason as mine were original after 200K miles. The change was night and day.
 

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How often do we need to change the ignition coils? Mines have 100k miles but car runs and idles fine.
 

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Discussion Starter #19
I left the car at my mechanic's place to change the wires and the tensioner shock.

My mechanic told me that after they changed the wires, it was only slightly better.

They found two vacuum leaks:
1) the EGR valve has a broken membrane and lets air through; they plugged the vacuum line going to the EGR valve; I don't know if it is OK for the engine to run with EGR valve in one position all the time...
2) the hose connecting the lower and upper part of the intake manifold was loose (even though I had it tightened up a year or so ago); they told me that car started running normally after they tightened up this connection - still it's all greasy and probably should be replaced

I think I will have to dissassemble the whole intake manifold myself, check the prat numbers and replace all the seals and gaskets...

This EGR valve is what really upsets me. It's very expensive. :(

The car runs very smooth now, but somehow louder when accelerating?
 

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Discussion Starter #20
OK.

Today the rough idle came back. It was entirely caused by the rear connection between the lower and upper part of the intake manifold. It leaked air. After setting it in right position and tightening the problem went away.

The car runs smooth now.

I checked the EGR myself and it leaks vacuum a little bit but still opens and closes, so I reconnected it.

The engine runs a little bit diesel-like. Like if there was a little diesel somewhere between the 4th and the 6th cylinder.

Timing chain?

Also - I noticed sth, that I don't recall to happen before:

When I rev a little bit in park and then lift off the pedal, I can hear a whizzz sound. Like air under pressure - only while the revs are falling.
 
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