Thanks that helps my understanding a lot, I was thinking the valve cover could be a potential vacuum leak.

Drove it around the block to reach temp and observe gauges….then let it idle in driveway.

idling in P it moves between 600-1000 rpm sometimes it’s a surge others it’s more subtle variation, when I shift into R it drops to about 600, N same behavior as in P. D it flutters a bit from 600-800 and flirts with 500 from time to time. I got it to stall downhill again on test drive, seems the excess load from stopping on an incline is stalling the car out, again it will cut back on immediately. What voltage should the IACV read, rpm’s stay at 1000rpm when it’s unplugged

i have plenty of time and patience to fix this correctly so no worries. In the meantime I’m going to work to get that seized o2 sensor off before I attempt to adjust any thing

 

I would first concentrate on stabilizing the idle in neutral. It should not vary outside of 700-750rpm.
You need to decide if this is an idle control problem, or a if there is some sort of vacuum or mixture related instability.

I would start by wrapping a couple of thin copper wires around the male side of the IACV connector and hook up a DC voltmeter and tell us what you see, starting from cold start all the way to after the car reaches operating temp. Let's see if that looks normal. Do this all in neutral please so we are not confused about other gearing. In neutral there is no load on the engine and the load does not change over time.

Please list the following table:

Engine temp, RPM, RPM variance, IACV voltage, IACV voltage variance.

I need data at
right after cold start
engine at 40c
engine at 60c
engine at 85v (operating temp)

 

I would never say never. Loose oil can spew all over and can get into some pretty strange places and cause a domino effect.. I went with that because this new idle issue appears to be so very recent and it coincides with the recent work that has been done.. Of course anything and everything is always possible when trying to make a diagnosis.

 

Okay dolucasi, I will create a table with all of those values later this week.

i did the valve cover gasket a really long time ago before I knew about torque specs…it’s possible the oil did creep elsewhere, I’ll do a thorough check as I clean it up, i want to be sure those two injector ports didn’t get any inside them

 

You might also want to go to your local car parts store and pick up some engine dye and run that to see if there's oil leaking anywhere else that might be causing problems in a domino effect scenario in addition to providing the table that Dolucassi suggested which is also a good idea..

 

Recently purchased a 190 e in excellent shape. 1991, 2.3 , This is my second fill up and i had a lot of difficulty removing the fuel cap to refuel the car. Once I opened it I notice a lot of pressure coming out of the filler tube. Car runs fine. Starts up on fast idle as it should, then reduces ( to low though) Drives Ok, driven approx 450 since I purchased it. Last owner replace fuel take last year. Also, it was getting low on fuel almost at reserve level.

What could be causing this?

 

I also own a 1991 190E-2.3. It's pretty normal for there to be pressure when you're removing the fuel cap because the fuel tank is pressurized. The fuel cap is tight to prevent fumes from escaping. Not sure what you consider to be low idle.

 

I would be sure that the previous owner replaced everything (pumps and filters) and not just the tank depending on why the tank was replaced. The sending unit could be bad giving you false reading if it came out that old tank. In my experience with my car it would behave like it ran out of fuel at half a tank, but my tank was really bad due to 20+ years sitting. Like 190efan said the pressure is normal you might hear a slight hiss when screwing the cap off.

Seems we are in the same spot chasing an idle problem, too low in my case

 

here is the table, an additional observation is my car wants to almost immediately stall when I plug the IAC in then it’ll catch back up and surge a bit. These values are in neutral:

 

Thanks 190EFan, and BetterDaze for you info. On the next time I get gas, I will pay attention to fuel quality and see how the pressure is . I was just surprised in that I almost could not twist the gas cap off and they felt the pressure. Again than

 

Not sure why you are getting flashes of significantly lower average voltages. It could be a real issue with IAVC control or an artifact of a Voltmeter that i having trouble averaging properly.
My voltmeter and IACV does not do that.
Does the lower voltage otherwise ( not the flashes, but the ranges) coincide with the lower rpm? We are trying to determine if the lower rpm at any given temperature is caused by the lower voltage presented to the IAVC. So we are tying to see if the IACV is sticking or is the idle controller actually causing the surges.

BTW, it is perfectly fine for your car to almost stall when you plug back the IACV, you are giving the closed loop a shock and it takes time for the closed loop to settle. My car will stall every time I do the same.

You can try one experiment though for a decisive conclusion on this. You can tie three double A batteries in series to give you 4.5V, unplug the IACV and connect that voltage to the IACV.
The surging should go away and it should settle to a constant idle somewhere between 600-700rpm. If so, we can probably say the issue is the idle controller or the inputs to the idle controller.

 

By the way, how is your duty cycle doing. Is that behaving normally?

 

Honestly it's a bit hard to tell, I did not notice any hiccups or surging until I observed a voltage drop but I can redo the test. My DMM never displays a constant value...it does not flash those exact low values every time but I watched the multimeter drop below 4v several times. I just put the lowest observed "flash" per engine temp.

I'll try the AAA battery test next. At what engine temp should it be done?

my duty cycle should be okay, my indie checked before I installed all my new fuel and tank related components and could only really point at my "lazy o2 sensor" but I'm not sure how critical that'd be in this case

​

 

BTW, although there is no spec for IACV average voltage (for many reasons) the voltages you are getting are normal accept the large excursions and dips are not. You will get some variation because this is a closed loop system constantly trying to stabilize the rpms. The variations in voltage you are seeing and the dips are not normal.

Let's see how stable the idle is with a constant 4.5V presented to the IACV. Make sure the harness/plug to the IACV is disconnected when you hook up the battery, we do not want to damage your ECU.

My expectation will be that the rpm's will be rather stable with a constant voltage.

 

Perhaps I’m not connecting the 3 AAA correctly but the idle stayed at 900 the whole warm-up. With iac plugged in 650-800 constantly up and down.

it recently started displaying an o2 sensor light but probably from physical damage of me trying to remove it

 

Looks like you connected it just fine and it seems when you break the loop and apply a constant DC voltage your idles is steady as a rock.
So I would suspect there is no issues with your emissions control or vacuum leaks, neither ignition misses etc.

We will need to find out if the IACV is sticking or the idle controller is not steady for some reason. Applying a DC voltage to IACV is not the same as the PWM signal that it receives from the idle controller.

Any chance you tripped the CEL by unplugging the EHA connector?
If not, I would certainly check for error codes. Also double check duty cycle on the X11 connector (or check for average voltage)

 

Okay sounds good, I’m thinking I’ll try to remove and clean the iacv as well. But no I was careful not to mess with anything but the iac connector.

The o2 light only appeared after I tried to get the sensor off but that thing is so far gone…the top of it spins freely and it’s likely disconnected internally. I’m contemplating on having an exhaust shop cut out the section remove o2 and weld it back in but saving this step for last.

would like to double check duty cycle, my old indie did make some type of adjustment before I installed new fuel components and through my research it seems this shouldn’t really be done with a bad o2 sensor

 

Actually, such an adjustment as what your old indie did shouldn't be done period. This adjustment just might be at the route of your problem. I don't recall you reporting these symptoms before you installed your new fuel components. If you know your O2 sensor is bad, I would go ahead and change that and then see how your car behaves with the new O2 sensor.

 

My car did have the same symptoms before but without a clean fuel system it didn’t make sense to keep fishing at the time. I just called my indie and it actually wasn’t adjusted it was just reported as running lean and o2 was lazy. Their latest notes were looking into ignition timing/EZL and the o2 sensor.

Do the ezl and distributor cap communicate or connect in some way? I’m going to order a cap and rotor this week. I am throwing some parts at the car but these are things it would need anyways

 

Thanks for the clarification. I think I would start with the O2 sensor first since your indie has flagged it as being lazy. Unless there's a clear sign of moisture in your distributor cap, I would hold off replacing it until after you see how it behaves with the new O2 sensor. Your car is likely running lean because your ECU is trying to compensate for the lazy O2 sensor.

 

Don't waste your time on the ignition components. We already proved that it idles perfectly when the IACV is presented with a steady DC signal. So your ignition is not an issue at the moment like I comment in the last post.

Your next step should be to either go to a JY and take the exhaust pipe section (after manifold up to and including the O2 sensor) from a car so you can use it or remove yours and have the O2 sensor taken out. But again this will not fix your idle issues, it will only make your car run properly with the right lambda value.

Remember the idle controller is completely separate from the emission control system. In later models post '90, Mercedes even separated the electronics that were together in the ECU.

I would not do anything else prior to replacing the O2 sensor. Not even clean out the IACV. Cleaning them, if not done properly would lead to more problems if not flushed out properly.
How do I know? I have done it and mine started to stick AFTER a cleaned it.. Was fine prior to flushing it.

- Cheers!

 

Understood! that helps things come full circle. There’s a shop I trust close by that can help me get it off next week, won’t do anything else until that’s out the way.

I do have a few questions for my own understanding in the meantime…so as it stands I’m thinking the o2 sensor is causing a lean fuel mixture and wouldn’t a lean or at least inconsistent fuel mixture influence idle/running?Or does the EHA do well enough job on its own to keep it within parameters?

Imo the idle really isn’t that bad the main concern is stalling when coming to a stop. I’d still like to at least observe the lambda for my own knowledge. How is it done with the DMM?

 

Anything is possible but in your specific case we proved that your idle issues are not ignition or fuel related with the experiment we ran.

A bad mixture and 02 sensor would most likely have running issues, not idle issues but if it were so bad it would cause idle issues too I suppose.

In your case the instable idle and the stalling when come to a stop are probably related and if you fix one the other will most likely go away.
It is hard to diagnose stalling issues as it is an intermittent and momentary occurrence. Unstable idle is continuous so we can observe it.

You observe the Duty cycle just like you observed the IACV voltage. Connect your DC-voltmeter to the pin 3 to pin 2 on the X11 diagnostic port and measure average voltage and divide by the system voltage at that given time. That I believe is pin 6 to pin 2 but do not quote me on that. This is all assuming you do not have duty cycle capability on your instrument. If you do, just dial it to duty cycle and then you do not have to do the math.

After you fix the known issue which is the O2 sensor, we will continue the diagnostics, as it will not fix your idle in my opinion (it may fix the stalling, but that could be wishful thinking)

Happy Thanksgiving

 

The o2 sensor has been replaced but I haven’t had a chance to do a thorough drive in low traffic yet. It seems to be running a bit better though.

what can I test next?

 

I would suggest doing the drive in stop and go traffic. That should give you a good idea of where the car is now at with the new O2 sensor. Once you've done that then begin to think about next steps if the car still isn't 100%,