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Uneven idle, hesitating when accelerating, power is down

The title says it all. I've had this problem for a while - idle is uneven - engine is shaking a bit, it almost feels like it's missing, at certain throttle positions the car hesitates when accelerating, and - at least I feel - the car should be quicker. A friend owning a w124 E36 says the same.

The car in question is a 1993 500E, 171k miles.

What I have done:
Replaced S29/3 Idle switch at accelerator pedal (Mercedes)
Replaced S16/1 Neutral Safety Switch (Mercedes)
Replaced Brake Lamp Switch (Mercedes)
Replaced vacuum seals between lower and upper intake (Mercedes)
Replaced rubber between ETA and MAF (Mercedes)
Replaced a few vacuum hoses here and there, checked the entire vacuum system in the engine compartment
Replaced gasket between intake and ETA (Mercedes)
Replaced intake gaskets (Mercedes)
Replaced distributor rotors (Bosch)
Replaced distributor caps (Bosch)
Replaced distributor dust covers (Bosch)
Replaced spark plugs (Mercedes) - they are the correct for the car (Bosch F8DC4)
Replaced spark plug wires and coil wires (Bosch)
Replaced the oxygen sensor (Mercedes)
Replaced air filters (Mercedes)
Replaced ignition coils (Bosch)
Replaced catalytic converters (brand new from a company in Germany)
Replaced LH-module with an early one with WOT
Replaced fuel pressure regulator (Genuine Bosch)
Replaced intake air sensor (Mercedes)
Replaced MAF (used refurbished Bosch-unit)

I checked the MAF with STAR C3: Values are 1,50V and 21,8 kg/h at idle. Voltage rose to 2,0-2,1 at 3000 rpm.
I have checked the fuel pressure; it's 3,65 bar with vacuum @ idle, rising for a second if I press the accelerator and then going back to about 3,65 bar (with vacuum).
After shutting the engine off it stays at 3,65 bar for at least one hour (that's when I disconnected the metering device).

What I have not done/ought to be investigated:
Smoked the vacuum system
Tested the EZL

As far as I know I don't have any fault codes now.

What else haven't I checked? Where do I go from here?
 
Last edited:

emerydc8

Active member
I experienced a similar acceleration issue with my E420 last month. This happened right after I changed the spark plugs with new MB F8DC4, gapped to 1mm as per Klink's SOP. I noticed a rough idle which seemed to go away after driving, but there was still a hesitation while accelerating, especially when the engine was hot. It was almost as if the ignition module was retarding the timing as it tried to accelerate. I could tell it wasn't accelerating linearly. At first, I actually wondered if the transmission was slipping.

I installed another new set of factory F8DC4 plugs and the problem completely went away. So I don't know if it was a bad plug, right from the factory, or whether one of the suppressors just wasn't making good enough contact. I checked all the wires for resistance and they sat right at the 2K Ohm range, so I don't think the suppressors are bad.

Has anyone experienced a bad MB plug right out of the box? Are German-made plugs better? Neither of the plug sets I installed was from Germany. Both were from France. In any case, plugs are cheap. Maybe try installing a new set in addition to checking your insulators behind the rotor caps.

If you think the cats may be plugged, I did a post somewhere on this forum on checking the back pressure using a vacuum gauge tapped into where the HVAC pods sit.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
MAF values, as a VERY ROUGH guide, will be: 650rpm idle = 20kg, 1000rpm = 30kg, 2000rpm = 60kg, 3000rpm = 90kg. Within ±10% of those numbers would be fine. If you see anything radically different, the MAF is suspect... the oiling doesn't help either.

The catalysts should be silent when you whack them hard with your fist. If there is any rattle, the cats are also suspect. A proper test requires an exhaust backpressure gauge that you can view while driving at full throttle (this is important - can't check at idle, can't check in your driveway). That may explain the reduced power, but not the uneven idle.

The uneven idle could be a vacuum leak somewhere, a smoke test is the easiest method to find leaks. In the meantime, keep driving the car, give it some full-throttle time through the gears, and check codes frequently on all modules (with SDS / HHT-Win, use the Quick Test).

Oh, it would help if you mentioned the year / model being discussed here...

:cel:
 

Eno

Active member
Have you pressure tested all the injectors to check if they are working properly?


Sent from my iPhone using Tapatalk Pro
 
Status today is that the car runs better, power is up, however you can feel that there are some small misfires at idle only - and only then.
The car has got zero fault codes.

What could be causing this? A bad EZL? Could there be something I overlooked?
 

Trae

Active member
Did you test resistance in each suppressor @ 2,000ohms, and were the F8DC4s gapped to 1mm as per Klink?

The only time I have experienced misfire @ idle, not counting caps and rotors, was because I had a bad suppressor or too narrow a gap spark plug.
 
Last edited:

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
It's definitely not the EZL. Top items to check are what Trae listed above...

:shocking:
 
Actually no. EPC lists the spark plug gap to 0,8 mm. I gapped them all to 0,9 mm.
It's not a bad misfire (cylinder cutting out completely), it's just... more like a small miss, and this is happening only when the engine has heated up.
I will check the suppressors when spring comes back to Norway - the car will be put into winter storage tomorrow :)

Edit: I’m not opposed to regapping the spark plugs to 1,0 mm, however what is the reason for doing that when Mercedes recommends 0,8 mm?
 
Last edited:

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Edit: I’m not opposed to regapping the spark plugs to 1,0 mm, however what is the reason for doing that when Mercedes recommends 0,8 mm?
There's detailed discussion on this in a thread a few years ago, if you search you can find it. Short version is, when the engine is hot and the mixture is lean, the gap is too small and the spark created has trouble fully igniting the mixture. Opening up the gap helps reduce the hot-idle intermittent hiccup. It may not cure it, but it should help. From memory, the Klink/Jono recommendation was to open up to 1.0-1.1mm.

Also... if your engine mounts are old, that can amplify the feeling of the hiccup. Bad news is, replacing mounts is not a fun job, and the only good mounts available now are OE/dealer, at ~$450/pair from discounters. Search for threads on this if you need to replace the mounts.

:mushroom1:
 

maw1124

E500E Enthusiast
Did you test resistance in each suppressor @ 2,000ohms, and were the F8DC4s gapped to 1mm as per Klink?

The only time I have experienced misfire @ idle, not counting caps and rotors, was because I had a bad suppressor or too narrow a gap spark plug.
A year or so ago, my guys noticed a “slight miss” that I hadn’t, and replaced caps and rotors as a result. I’m not mad at that, but I’m keeping this post handy, as next time I replace plugs, they’ll be gapped to create a larger spark. Question: can simply running a hotter plug help?

maw
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Question: can simply running a hotter plug help?
maw, a hotter plug would help keep the plug clean, if fouling were an issue. But that is a different issue, and generally not a concern. I run a colder plug than normal in one of my cars and have never had any issues with fouling. In general the M119 has no issues with fouled plugs unless something is really messed up on the engine. Put another way, heat range and gap are adjustments/variables for two very different concerns/issues.

:rugby:
 
Did you test resistance in each suppressor @ 2,000ohms, and were the F8DC4s gapped to 1mm as per Klink?

The only time I have experienced misfire @ idle, not counting caps and rotors, was because I had a bad suppressor or too narrow a gap spark plug.
Excuse me for being a retard, but do you mean the resistance in the suppressor should be 2000 ohms, or should I set my ohm-meter to the 2000 ohm-setting and see what I get?
Again, I'm sorry for being a total tard :p
 

Trae

Active member
As long as you test the resistance from the cap to the end of the boot that attaches to the top of the spark plug it should read 2000 ohms of resistance +/- 100 ohms.
 
I forgot to mention - can this problem be - at least - partially caused by a bad MAF? When I got the car it had some reusable air filters with oil, and the MAF was not looking pretty (dirty, oily etc). It was cleaned with MAF cleaner and the values in Star C3 are correct - but still?
 

JCM1

Member
Hi Little-e:
Rennlisters are strongly against the use of reusable oiled air filter elements for exactly that reason - oil gets on the platinum wire and despite a high temperature residue can remain. I had used an oiled fabric air filter and now run a paper filter in my 928 GTS and have had no MAF issues.

All the best,

Joe
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Over-oiling those type of filters can cause problems, but if PROPERLY oiled, they don't hose up the MAF. I have K&N's in a couple of cars with zero issues. The problem is almost always caused by people not following the clean / re-oil instructions and grossly over-oiling. If you watch the K&N manufacturing video, it's interesting to see how little oil they apply to new filters.

Anyway - if kg/hr values are normal in live data, it's highly unlikely the MAF is causing you any grief.

:hornets:
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Can these problems be caused by a blocked EGR-pipe?
I don't think so. Generally, if EGR isn't working due to the valve not opening, or the pipe clogged... you just get a CEL (on USA models) and possibly an error code somewhere. But causing reduced power, I can't see how that could happen.

:scratchchin:
 
So this thread has been down for a while, thanks to gsxr for answering me on PM btw.

I have scanned the car with HFM-scan and I have found the following:
"O2S 1 (before TWC) (G3/2) not operational or defective, open circuit "
(this appears only at idle)

The car runs super rich
HFM-scan reports a voltage reading of 56 mV at idle, I can't remember what it was during driving, basically outside the oxygen sensor's reading capabilites.
How that is possible I don't know.

What could lead to this? The oxygen sensor is brand new, and it was the same with the old one so I can rule that out btw.
 
Last edited:

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Can you check codes and live data with Star instead of HFMScan?

Assuming the error and O2 data are accurate, the O2 voltage is showing extremely lean... in which case the LH module is trying to richen the mixture to compensate.

Do you have a spare LH module to swap out? I'd try that next.
 
I have already tried a different LH module, the car acts the same. The module I'm running now is a module with WOT-enrichment, and the car runs better if I floor it. With the original module it does not. I would say the fault is not within the LH-module, since (taken away the WOT-enrichment) the car acts the same.

I might have access to Star C3, but not readily available. It takes some time to arrange.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
At this point I would check for codes on all modules, and see which codes return after clearing. Something really weird is going on.

Did you ever check MAF readings on live data, using the values I posted above?
 
I checked the MAF last year, and at 646 rpms it measures 21,8 kgs. Hot wire voltage 1,5 Volts. This was done using Star C3.
It should be good, right?
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Yes, at least at idle, that number is ok. The MAF really should be tested at various RPM's, holding a steady RPM to see if the kg/hr reading is also steady. I doubt this is your problem though.

Does this car have a new/updated upper engine wiring harness?
 
Okay, I will do that as soon as possible.
The upper harness is dated sometime in 2008 (March if I remember correctly), and the throttle body has a date code of 02M06 if I recall correctly. The harness doesn't show any signs of cracking as I have seen. I have replaced a couple of connectors.

I checked fault codes with the blinker thingy last fall before I put the car into storage, and there weren't any. I will recheck.
 
Just a small update - I rechecked the tag on the wiring loom today just to be sure.
It's a Mercedes-Benz tag dated 25.03.08 so it's good. However the part number is A1245439526 (up to ident B 840526).
My car is B 927630 and as such I should have A1244402006 (from ident B 840527).

Could this be the root problem - or isn't this really a concern?
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
...the part number is A1245439526 (up to ident B 840526). My car is B 927630 and as such I should have A1244402006 (from ident B 840527).
Could this be the root problem - or isn't this really a concern?
Shouldn't matter... other people have reported interchanging the two harnesses without any issues.

Question - has the engine ever run properly? Or has it acted up ever since you bought the car?
 
Okay. So the harness is a dead end.

Well. I don't think it ever ran properly when warmed up. Something happens when the engine gets to about 60 degrees, and gets worse after that. When it's cold it pulls strong and it's smooth as silk.

So it probably has a bad vacuum leak (although I have replaced just about everything) or the lambda control is totally wack-o.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
I think someone else had an issue where the car ran great when cold, but then acted up at operating temp. They replaced almost every part you can think of with no change. IIRC... the culprit turned out to be off-brand, no-name ignition coils? There was a long thread about this, maybe early last year... car was an E420 but the components are all the same. I don't think this is your issue though.

:scratchchin:
 
Yeah, I've also replaced the coils with new Bosch units with no change at all. The car smells fuel (when warm) but the o2 voltage reports a lean mixture. I need to check with Star or a multimeter to see if the cables from the o2-sensor to the ECU are good.
 

195910

Intl 500E GTG coordinator
- Disconnect the O2 sensor and see if it runs any better, it will not run perfect but it should not misfire.
- How are fuel injectors ?
 

195910

Intl 500E GTG coordinator
Vacuum leak is more noticeable when cold as idle fluctuation.
Your issue seems to be when system is in Closed loop, where the O2 sensor is giving a lean mixture signal to the LH which responds by dumping fuel. If O2 sensor is functioning properly (see readings at different RPM, after 30minute drive), then its compensating for an actual fuel flow problem.

Have a look at the injectors if O2 sensor is fine
 
I have tried two different oxygen sensors, one OEM Mercedes and the current one is a Bosch unit (not a universal unit) and there is no difference. If there is a problem with the oxygen sensor it must be in the wiring inside the car, not the oxygen sensor itself.

Let's say the problem is ignition related. An ignition problem starts to appear due to heat making a small misfire at idle and low power due to a weak spark causing poor combustion. The oxygen sensor will try to compensate by leaning the mixture, thus giving a false reading of a lean mixture.

True or false?
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
If the system tries to lean the mixture, the O2 sensor would read lean, if it was actually able to lean the mixture. If it can't... and the mixture remains rich... the O2 sensor is still going to read rich. A good O2 sensor can't give a "false" reading, AFAIK...

:scratchchin:
 
I see. I will measure the oxygen sensor and that the wiring is actually not shorting. If that checks out the injectors will be checked.
 

195910

Intl 500E GTG coordinator
- Spark misfire will be rich values at the O2 sensor, the LH with subtract fuel.
- Two different O2 sensors and both giving lean, they can't be shorted if they are giving reading within range.
- Could the heater circuit be faulty ? this you will need to check with a laser thermometer and the car at Idle.
 
As already reported I'm getting the following message *only during idle* with HFMscan:
"O2S 1 (before TWC) (G3/2) not operational or defective, open circuit"

If the error message is an actual one, why am I not getting it during all conditions?
I will try to use Star as soon as I can get hold of it.
Btw, why do I need a laser thermometer? The heater circuit cannot be measured with a multimeter?
 
Today a friend and I measured the wires from the lambda sensor connector (the lambda sensor is a brand new Bosch unit, and it was the same with the old 1-year-old Mercedes unit) to the LH ECU. The wires are fine.
Nevertheless I'm getting the following fault codes:

Heated oxygen sensor inoperative
Idle speed control inoperative (this one I've never seen before)

Star (eBay-unit) will arrive in a few days, so I will check more thoroughly.

Could my ETA be on the blink and causing these issues?
 

gerryvz

Site Honcho
Staff member
I believe the "idle speed control inoperative" is a throwaway code.

The ETA won't have anything to do with an O2 sensor code.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Are you getting these codes using a blink-code reader or SDS...

...or ONLY seeing the code via HFMScan?
 
HFM reported these. I did the blinker codes just now and here are my findings:
Pin 6:
11 + 17 (wouldn't clear)

Pin 30:
3 + 8 (I've seen 8 a couple of times, so that has to be investigated)

Pin 17 wouldn't read. No other fault codes.

I'm still waiting for Star :)
 
Last edited:

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Pin 6 (ASR) code 17 is for low battery voltage. Have you checked/cleaned the positive battery terminal, specifically the smaller (10mm?) nut that holds the wire which powers the CAN modules directly?

Pin 30 is SRS which has no connection to any powertrain systems; however this is also indicating a voltage supply problem. Trace the source but I'd wonder about the ignition switch.

Odd about pin #17.

Remember that HFMScan may report "current" faults which do not get stored; these may not necessarily indicate a problem. Current fault codes are not the same thing as stored fault codes. SDS would definitely help.
 
Could pin 6 fault 11 also be a voltage problem? Or is the relay on the blink for sure?

Since I'm not able to connect to my EZL, should I be worried?
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Pin 6 code 11 could possibly be related to 17, but I'd see if you can get 17 fixed first.

EZL connection is probably something between the diagnostic connector and the EZL, not the EZL itself. I'd be more concerned if SDS can't connect either.
 
I see. Even though my engine wiring loom is dated March 2008, it does not have a Delphi tag. Should I be worried? The date is on a Mercedes tag along with the part number.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Nah, if the wiring harness is not original, it should be fine. These were only available from MB, there are no aftermarket versions (unless you rebuilt one at home). Also, the engine harness would not affect communication with the EZL for codes.
 
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