320E M104 engine, Idle problems
 

The car has been running beautifully for a number of years and then all of a sudden it started to stall at tickover and has a very rough idle. It starts first twist of the key hot or cold and after the air pump stops the idle becomes rough and finally stalls. It also accasionally appears to shut down for a couple of seconds when cruising with around 2000 or less rpm.
I made the code reader and got the following codes from the 16pin diagnostic module.
Pin 8
code 3 air intake temp sensor
code 4 hot film mass air flow sensor
code 13 O2S(lambda) control operating at rich or lean limit

Pin 14
Code 2 Cruise control/idle speed control module
Code 5 stop lamp switch
Code 11 fuel safety shut-off to LF-SFI control module

I have over the past couple of years replaced the wiring loom and the throttle module, cruise control works fine (throttle module hums with ignition on ?). Plugs and coils are fine. I have never looked at or cleaned the EGR valve and pipework. The EGR diaphram appears to be ok as I can actuate it by sucking on the vacuum line, there is no vacuum on this line at idle (is this correct).

My question is where do I start to chase this problem down. Is there anything I should try first or is there further tests I need to do before I start to replace things. You help wold be appreciated.

Search " OVP relay" and pull the vac line off the FP regulator and see if there is gas in the line.

Thanks, I've swapped the OVP relay and no change there. Will check out the other test. I have reset the codes and will check again after a drive.

I had several of those same codes on my '93 2.8 liter M104. It required a new MAF and O2 sensor to fix things up. Based on your description it sounds like the engine is running on the default fuel map - basically not using either the MAF or O2 as inputs to control the fueling. My car was doing the same. And it ran surprisingly well, though the idle quality was lousy - rough and surging, though I don't recall stalls.

In my case replacing the MAF cured the pin 8/code 4 and the driveability improved greatly. The idle was still loping however. Replacing the O2 sensor smoothed out the idle. The car had 120K miles at the time, engine wiring harness had already been done. Throttle actuator is still original (and I'm scared to touch it...).

- JimY

Thank you both. To reply to Arthur, I pulled the vac line of the FP regulator and is clean as a whistle no fuel leaking. I have given the car a good run after resetting all the codes, stalling many times and getting poor power at low revs. Check the codes again and got the following results.

Pin 8
code 4 MAF sensor
no other codes.

Pin 14
Code 1 All clear

I may have set off some of the previous codes as I have been checking plugs and coil and other electrical connection to make sure all were contacted well.

Does this now mean there is a faulty MAF sensor, can I check it out easily or give it a clean or should I bite the bullet and replace it?

Thank you Jim Y for your help, My problem does indeed seem similar to yours.

Mike

Carefully check ALL the vac lines and their rubber connections. The plastic lines become brittle and develop pin holes. The plastic lines can be replaced with any high temp rubber hose.

Switch Over Valve aka "SVO" is located front of engine. Tests for it and o2 sensor.

W124 M104 Idle problems
 

Its been a while since the first post of my problems. I have replaced the Air Flow Sensor with admittedly a second hand one which I was confidently told was working perfectly. It certainly looked far newer than the one it replaced. After fitting the engine performed almost as good as new, the stalling and low power were immediately banished. However the idle while much improved still was a bit lumpy when in Drive with revs below 600rpm. In Neutral revs were around 600-700rpm and much smoother. From cold the idle was smooth and only started to hesitate when hot. For much of the time there is no problem and then it goes into a rough patch with some surging due to the engine management increasing the revs to prevent a stall.

I have done some checking of the codes with the LED device as this is what I have found.
Pin 8
Code 4 Air mass sensor
Code 13 OS2 control system too rich or lean

Does this mean that both the AMS and the O2 sensor are at fault or can the O2 sensor cause the Code 4?

When I cancel the codes and take the car for a run I only get the Code 13. But after a longer run or a few days I get the Code 4 come up as well.

I am reluctant to replace the AMS if the problem is with the O2 Sensor. Also does the O2 sensor cause the Code 13?

As always your help is much appreciated.

I have seen both code come up if there is air leak or some loose contact in my M111 (Assuming all sensors are fine.)

1) Re-check and clean AMS connector contact points.
2) Check if there is leak @ IAT plug.
3) If there is breather that goes into intake/crosspipe from cylinder head cover, check for crack.
4) Check vacuum lines.
5) Check brake booster vacuum line, it has one way valve which can leak (for testing just disconnect brake booster pipe, block it temporarily clear codes and check).
6) Check purge valve lines for leaks, check if purge valve itself is stuck open, you should not be able blow air through it when removed. Purge valve operates @ temp > 80, you can feel it ticking if you touch it.

I have seen only blocking purge valve line for testing will not work, since purge valve is electrically connected, ECU's fuel injection timing will be as if purge valve was working. Blocking purge and disconnecting it electrically should work, but ECU puts up error code for purge valve connection open.

Code 13 is not 02 sensor code..it is the lambda system code.

So, it is either lean or rich, meaning an intake air leak or improper fuel pressure.
So... you are back to looking at the FP regulator along with possible intake leaks. I would take a full FP test, specially the OFF hold testing.
There are two other possibles ..one is dirty injectors [ run some cleaner thru for a tank] and the other is an internal vac leak..these are hard to find and usually are the EGR is not seating well or the Purge Valve is leaking by...that one is common b/c they get full of crap and stick open.

Thanks Arthur. My next question was whether Code 13 indicated a O2 sensor fail.
I am suspicious of the EGR valve and pipe as it has never been cleaned out, its one of those maintenance issues I have been putting off for obvious reasons! If I suck on the vacuum line I can hear the diaphram opening and closing.
I am also suspicious of the changeover valve under the cover at the front of the engine but not sure on how to check it. The vacuum connectors are good and tight but do not know under what engine conditions the valve switches over?
As codes 36 and 39 are not showing I presume they can be faulty without registering to the diagnostics.

I bet just tuning the thing up will work...new plugs, cap, rotor...screw the codes....the codes...bullcrap

I swear, I have owned so many German cars over the years and all of the little warning lights and signals are so full of crap that I can't even go into detail here. Screw the warning lights...pretend as though your German Mercedes/BMW/Audi/Porcshe is a Ford and look it at that way.... if it's leaking oil, fix it....if it needs coolant, do it...if it needs brakes then take care of it....these cars are simply cars...a Mercedes is exactly the same as a Chevrolet in principle...same thing...don't be confused and overwhelmed.....by the name...screw it...they are all just cars....

:bsflag:

He's not talking about "warning lights." He's talking about codes read from the computer module(s). They can be of great value in diagnosing problems. In fact, that is what they are for. Ford and Chevrolet have the same provisions.

Thanks guys for your interesting comments. Todays cars have more sensors than an intensive care ward at the hospital and diagnostics are imperative. Whilst the codes can be confusing I would be clueless without them. Still there's always the challenge of sorting the problem out!

Update? I'm assuming since no post in 2 months that it is fixed. What was it?

No the problem is not completely fixed. I have cleaned the EGR tube (what of a job)It was not completely blocked at the inlet end so I'm not sure what effect this would have. I have checked the Purge Valve and that is working properly no crud in it and pulsing OK. I have just this week replaced the MAS with a new BOsch unit. I have checked all vac lines that I can see especially at the SOV, all appears perfect, no cracks no leaks.

The car is running very smoothly with the new MAS with a noticeable increase in power,but idle is still not quite right, it feels like the mixture is weak which does suggest an air leak somewhere. Will check HFM codes after running for a few days and see if any codes return. My next task is to remove the EGR valve and see if it is seating correctly. I can hear it opening and closing when vac is applied but do not know if it is leaking in the closed position at idle.

If any one can think of anything else to check I look forward to hearing your comments.

I have noticed recently that the upshift delay from 2nd to third gear when cold has increased and I now have to drive half a mile before the tranny upshifts or let the engine idle for 5 minutes before driving. I dont think this is connected to the idle problem but who knows? THanks