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Idle Problem That Fixed Itself.........almost.

4661 Views 141 Replies 6 Participants Last post by  LauraS
Today on my way into town I stopped at a stoplight which was red and the engine ideal wandered up rom about 500 to 750 RPM and seemed to have an ignition miss or something. I was a bit worried that it would stall but it didn't and once I accelerated the engine ran fine. This happened about 5 times when I had to wait for red lights. The temperature gauge read 90C and the ambient was about 22C. When I got to my destination I left the car for about 1 hour and when I returned the car sputtered but did start and settled into a nice 600RPM idle and from then on all of the way home it ran just fine? I have no idea what happened. Does anyone have any suggestions ? I would like to know of maybe the ICV might have been sticking or something else to look at.
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Engine only able to start when cooled down could point to ezl failure. Do you have a spare ezl to try out? Perhaps borrow a known good unit some someone
I would agree, if you believe you are experiencing ignition misses, and failure to start due to ignition and you already verified the CPS is within spec, the EZL would be the next item down that path. I do not see the coil being an issue only when warm.

Unfortunately, you will need a spare EZL as a trial and error. This is assuming you do not have ans access to some sort of analyzer or scope to monitor the ignition.
No Anayzer or scope etc but I do have a spare EZL somewhere. Once I find it in my cluttered garage I will replace the one in the car now. The spare is suppose to be good. I guess no way to tell except by trial and error?
i found the spare EZL but the white paste is pretty dried out. I guess that I will need to source some heat sink paste before I install the unit. i wonder of the heat sink dried out in my EZL and caused the problem. Maybe refresh of paste will restore it back to reliable operation since it seems to be heat related.
The nylon backing generally protects the heatsink paste for a long time before they dry completely.
Perhaps remove yours and see what it looks like. It is easy on easy off.
I removed the old EZL and the heat sink paste is pretty dry. i am hestant to install the spare EZL until I have it coated with heat sink paste which I will try to source next time I go to town. No sense in destroying a piece this valuable just to be in a hurry.
I sources two small packets of heat sink paste at an electronic store while in town yesterday. i applied it to the spare EZL according to instructions found on the W124 forum. The car started and idled fine both cold and warm but I havent taken it on the road yet. I hope this solves the problem but if it is the EZL I will try ty to find another spare!
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Looks like it is fixed? Cool
Well I am not sure the problem is fixed as it does seem to come and go. I did finally get a chance to take the car for a length drive today and the idle and acceleration seemed OK but it doesn't start so readily when cold or hot and on two occasions when accelerating from a stop sign the car engine stumbled a bit before smoothing out? I did put a bottle of Gumout Fuel System Cleaner with P.E.A so maybe it is doing something that is adversely affecting the fuel system. Anyway I am reasonably confident that the car won't let me down for the time being. I may have the cold start valve and fuel pressure tested when in town.
I would beware of any gas additives as they can wind up doing more harm than good. Mercedes-Benz is very opposed to the use of such additives and so was my engineer father. Gasolines today already have cleaning agents in them. I would suggest you check your fuel filter as it might be clogged. Also be sure that you're only using premium gas. You should also take your car for a regular highway trip as short, around town only trips can be detrimental to your car and cause carbon build up that's not getting blown out by highway driving.
w201fan, The filter was installed less that 5000km (3000miles) ago. I only use premium gas (91octane). I live in a rural where all of my trips involve highway driving.
I have had good experience with certain additives in my vehicles, boats and aircraft.
As for your hesitation at traffic lights, I used to get those intermittently. Upon checking the arm and distributor, they look pitted. In the end I replaced the distributor and arm. I have not encountered it since replacing them.
ewee, The cap and rotor were changed not 3000 miles ago with Bosch parts. The hesitation only happened twice in a total of about a dozen starts.
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w201fan, The filter was installed less that 5000km (3000miles) ago. I only use premium gas (91octane). I live in a rural where all of my trips involve highway driving.
I have had good experience with certain additives in my vehicles, boats and aircraft.
I just wanted to rule out a fuel issue being the explanation for the hesitation. As for not using any fuel additives, I tend to go by the recommendations of the MB engineers as well as my engineer father who had more than 40 years of engineering experience.
Well the stuff is in the tank now. My late husband was an air engineer as well as an airforce and commercial pilot and used gas additives in his aircraft and vehicles approved but not recommended by Transport Canada as I recall but honestly can't say which. We used Seafoam in our outboard engines for many years also. It might not have done any good but didn't seem to do any harm.
In any event it is a wait and see at this point since I am not going to syphon the gas from the tank. Thanks for your advice.
I am going to check the CSV and the Temp switch to see if I am getting a shot of gas at the cold start as it seems to be a lean mixture. This happened only after I switched the EZL module. Before the incident when the car wouldnt start the engine always fired up on the instantly.?
If I were you Laura, I would just focus on the new EZL for this issue. It may have something to do with the new EZL. For starters make sure your timing is correct using a strobe light.
Did you use the nylon backing when you applied the paste to the EZL? Is it easy to swap the original back in? By the way I believe you can just unplug the old one and connect the wires to the new one (without mounting it) and crank to see if it starts much easier. It will be fine to operate for a few seconds (or minutes) without the heatsink coupled to the car chasis just don't leave it running for too long.

Are the two EZL's the exact same part number?

When one is cranking I noticed that the timing is different than when the car is idling, I do not know if this is intentional or an artifact of a very slow speed crank operation.
Well I did check the thermo switch today but could not get one of the 5mm hex bolts out with my neighbours help. I certainly did not want to strip that bolt!
The thermo switch read 2675 ohms at 18C which i ink it ok. With the ignition on it read 4.5 volts but being alone at time I could not read the voltage in start mode. the line to the CSV had pressurized gas so I think that is good. No I don't have any nylon pad between the EZL and the fender. If I remove this EZL I will lose the expensive heat sink paste.
It is odd that the old EZL seems to starting the car fine cold but rich when hot and this seems to be lean starting and hot. I may try to get hold of a fuel pressure gauge and see it that is OK. Thanks. Laura
An EZL can not make your mixture rich. It may have the wrong timing to make it feel like it is rich because there is unburnt fuel due to bad timing.

I would first focus on timing between the EZL's. Are they different? If so, why? Which one is correct?

I believe sooner or later you will need a strobe light. Pretty inexpensive at the auto stores. Perhaps your neighbor has one?
I do have a strobe timing light in the garage somewhere. So what should I be looking for on the timing marks when at idle and at higher rpm. Do I hook up the wire to the number I cylinder spark plug wire. The issue at the moment seems to be a lean mixture not a rich one?
Mixture and timing are entirely orthogonal issues. I should ask why you believe the mixture is tied to your EZL?
Mixture issues need to be diagnosed after the timing issues are dealt with.

The theory was that you had some intermittend (or hot) EZL issue meaning when the EZL got hot it was acting up.

The new one you put in does not seem to act up but it is harder to start and it has some stumbling in acceleration.

So it looks like you traded one set of problems for another with the EZL, and these units are not new so who knows the condition of your replaced EZL.

Your experiment was a very controlled case as far as I know and you did not change anything else. You did add that fuel additive which probably will do nothing but will not harm anything either.
I actually did that once because this specific additive was something that was sold at the Mercedes Dealership (something called BK-44 or something like that). So I tried it, it had no effect on the car's performance whatsoever.

Did you do anything else other than to change the EZL and add in some additive?

The timing should be 10 degree BTDC during idle. At 2500 rpm it should be ~30 degree BTDC but do not quote me on that. Perhaps post your results.
While cranking I have seen 20 degree or so, it is unstable due to low speed of the engine so hard to read. Also my car starts on a dime, so hard to record the results.

Yes put the strobe light electromagnetic sensor on cylinder #1 (closest to the radiator) and let's see how the new EZL is doing at idle. Rev it to 2500 rpm and tell us what you see there as well.
Recall the timing marks are in the front next to the diagnostic CPS below the distributor.
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