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

4653 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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Behavior as this are almost exclusively electrical in nature. And as Josh mentioned, if it happened once, you can bet it will happen again.
Sometimes it has to be persistent enough where it can be diagnosed.

One known component that does this is the OVP. If it is cutting in and out you will get that. Do us a favor and check the date code on your OVP.

It is the 1" x 1" x 3" relay that has fuses on top and is next to the FPR behind the battery compartment.
It is quite likely that you will need to keep driving the car until it shows the behavior more frequently. Mine kept stalling randomly once a week for 6 months until it started doing more often (every other day) and we found the problem eventually. Not a stall since in 3 years. So some persistence may be required.
I would eliminate the CPS as a possible culprit first. My understanding is that there is an expected range to the the CPS resistance (at the EZL).
If it is out of this range the ignition unit senses a fault and shuts off ignition.

Because the resistance is not constant between hot and cold if it is out of range either hot or cold the ignition will not fire.
Usually they are outside of range when hot and in that case the engine just shuts off and you have to wait till it cools down and falls in range again.

I would advise to disconnect the EZL end of that CPS sensor wiring and measure the resistance at cold engine and hot engine and see if it is getting too close to the limits.

Although that idle speed wandering does not sound like a CPS to me. As the CPS cut off is sudden and the engine will stall and not start again.
I read on the forum that the spec for CPS is 780 ohms - 1200 ohms.

Yours is well within the limits so I would strike that for the culprit list.

My system voltage heavily depends on what is on.
If everything is on it will drop as low as 13.0V.
By everything, I mean:
Aux Fans running (these realy use a lot of current)
AC, on with fan turn to position 2.

Otherwise if everything is off, it hovers around 13.5V once the engine warms up and the battery is charges. Starts out at 14.0V after cold start.

So when you measured 13.1V, what were the conditions?
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OK , We have DRL so on this car so all lights headlights and taillight etc are on at full luminance when ignition is on. I had the AC running and the fan at 3 so lots of load on a hot engine . It usually runs at higher voltage at first start uighur 13's. I so think its the alternator.
Yours is similar to mine. The alternator/charging system in these cars s a bit on the weak side and your results are expected. I do not believe your issue is your alternator/regulator/battery.
I think you have to determine "is this is just an idle issue or a general running issue?". If the car runs fine driving around town I would say your ignition components are fine.
Then you have to look more into idle/starting issues.
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.
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.
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.
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?
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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Hmm, it should move but should be visible, not sure why it is off scale like that. But at least the idle timing is just fine.
BTW, you do not need a brick on the pedal for next time, the throttle actuator is accessible to your free hand though it is a bit hidden under the air filter housing.

So at the moment you only have cold start difficulty?
That is purely a CSV not firing issue. As with a working one these cars start on a dime no matter what is happening with the fuel system in general.

That you will need to diagnose first electrically by disconnecting it and cranking and observing if a voltage is present for 1-2 seconds.
If you pass that test, it may be the CSV itself by taking it out of the car (reconnecting the electrical ofcourse) and repeating the crank test to see if it sprays fuel in a nylon bag.

Hope I'm not stating the obvious here....

- Cheers!
In that case you are fine. For future reference you can take the airfilter housing off and stand on the driver side fender to do this.
Also for others benefit the timing spec is:

9 degree BTDC at idle
33 degree BTDC at 2500rpm
It maxes out at 35 degrees.

I just measured my original and a spare EZL and got the same results on both.
It is interesting that the timing is not a continuous transition, it seems to go up a couple of degrees every few hunded rpm more like a second hand.

I had suggested checking the presence of a signal without taking the CSV off, now that you are having trouble taking is off. Had you done that before?
LOL, I did not mean "On" the fender Laura, just be on that fender side, instead of in front of the car. I just stood next to the fender and I do not have a long reach, you can do it. I am only 5'9".
w201fan, I am inclined to agree. I did get that stubborn Allen screw off and removed the CSV for testing. It squirts a small amount of gas when the ignition is turned to start. not sure if that is enough but it does click and open the jet when 12 volts is applied. I dropped a screw down into the oil pan area by accident and had to remove the splash shield to get it back and noticed that the timing marks on the vibration damper were right were I could see the TDC and 10 degree marks so I put a dab of white paint on both. I then rechecked the timing and with the engine in drive and the vacuum hose removed from the EZL at idle the strobe indicated more than 10degrees? Possibly about 15 degrees + or - . Is the too high? I have been reading about this and now wonder if my husband removed the R-16 resistor or if Canadian spec cars didn't come with one? One more thing to look for.
On start the engine fires immediately and then suddenly stops for the first try and then might start and run on the 2nd or 3rd try. It starts better warm than it has it quite a while though so I am quite pleased. I sure am stiff though after being under the car this afternoon. Maybe time for a trip away to do some fishing for a few days with the kids.
I believe your CSV is fine, they only spray fuel for 1 second or so just to get that initial start when cold.
If the car dies after that initial start, it generally is because your fuel system pressure is not building up in time. There could be many culprits for that but I believe you will need a fuel pressure gauge to diagnose that nuisance.

I can check how much the vacuum advance is for you if you like by doing the same.
I believe there is always pressure in the lines, just not much after many hours/days. So it would be difficult to gauge that without a fuel pressure gauge. You will need a metric adapter for the gauge which is generally harder to source that the pressure gauge itself.

When you acquire the gauge also purchase a set of fuse line pinchers, available at your auto stores. They are gentle on the rubber lines (as opposed to a clamp vice) and very cheap. You can pinch the accumulator line and see if the pressure maintains when pinched.

Your late husband probably had these in the garage though, you may not need to buy them.
Most of the reviews I read on fuel pressure gauges are negative. I need to take my never used, 40 year old pressure gauge out and give it a try one of these days.
As I also have a small leakage in the system.

You need a gauge with a scale of minimum 100 psi.
General complaints are the gauges are leaking right out of the box, product does not have the necessary couplings, etc.
I have not read very many positive reviews but then again, consumers usually only complain and do not write positive feedback.

For these fuel injection systems, it is recommended that a hook-up with dual input (one for system pressure the other for lower chamber pressure), a valve and a single output be purchased/put together. You want to be able to measure the difference between these two pressures and using 2 gauges is probably not a good option due to the inaccuracy in the meters.
Sure, we can ship you a trouble free Tesla made right here in Silicon Valley. And yes it should be worry free for 20+ years. If something goes wrong with it, good luck though, I doubt there will be anyone who speaks the language in a 500 mile radius where you are.

Back to your issue. You do not need a fancy set-up, I replied to a related but orthogonal question of diagnosing Fuel Distributor issues and what type of set-up is best. You do not have that issue.
Yours is going to be simpler.

Laura, when you start your car in the morning does it fire up initially but die or does it just have trouble even firing up? Perhaps we can see if we can help you a bit from afar.
You already verified a working CSV system, so you are halfway there.

- Cheers!
From 2000 miles away it sounds like your fuel pressure drops all the way down to zero overnight. The CSV does not need much pressure to spray fuel, even at less than half the needed pressure of 80psi it will spray. This is why your engine starts but dies because the FD is not properly working as the pressure has not developed.

Once it starts, does it struggle just a little bit before it straightens out?

The flooding feeling is probably because every time you start the CSV sprays again and some of the fuel must be un-burnt so stays in the intake.

What I would suggest is to get a fuel gauge and if you can not source the desired adapter to bolt straight into the test port of the FD let me know. I'm sure I can help out.
Also purchase the $12 pinchers at the autostore, they will come in handy for the next step.

What you will do is to monitor your fuel pressure in various scenarios and see how fast it drops (if it actually does) and how low it goes.
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