On my 1994 Mercedes E320 wagon,I am getting low idling so low it kills the engine. Troubleshooting on the DM Self Test Diagnostic Module (16 pin) indicated a code 6 meaning Idle speed control faulty. That is the only code showing using the DM.

When I use the code reader to retrieve the codes on the individual pins, the code reader shown these results:

Pin 6, code 9, SRS malfunction indicator lamp (A1e15) or time limit for DTC readout /erasing e

Pin 8, code 8: Idle speed control (ISC) system at upper or lower control stop or CC or EA indicates "limp home" mode

Pin 8, code 13: O2S (Lambda) control system operating at rich or lean limit

Pin 14, code 2: EA/CC/ISC control module (N4/1) or Safety contact switch (M16/1s1) or Stop lamp switch or Cruise control switch or Actual value potentiometer or Starter lock-out/back-up lamp switch or engine speed signal or vehicle speed signal or closed throttle position switch or safety relay in EA/CC/ISC control module.

In addition, my cruise control does not work, either.

I removed the throttle body and sent to repair shop. In addition, I ordered new valve cover gasket replacement, new throttle body gasket and throttle bottle cover to intake manifold. While I am waiting for the replacement parts to arrive, I wonder if I should get new 6 coils to plug boots, 6 new spark plug wires and 6 new spark plugs? When I bought the 1994 Mercedes E320 last year, very little history of the Mercedes was given to me. Since I already removed the throttle body, reasonance valve and about to remove the valve cover, do I, might as well, replace 6 spark plugs, 6 coils, 6 coils to plug boots, 6 spark plug wires as new? That way, the engine will have proper idling, eliminating some if not all, idling issues? Any other parts need to be replace as well that I am not aware of? How do I know and/or can tell if the 6 coils, 6 coil to plug boots, the 6 spark plug wires and 6 spark plugs are good that I have on now? Just thinking out loud. In addition, I did some research on the type of spark plugs and found Bosch F8DC4 as the only kind spark plug to use, no exception. Comments, anyone?

I just got an email from the repair shop that now has my EA throttle body. He said he saw bad wiring harness and bad clutch and takes 2 to 4 business days to repair.

The service repair technician sent me 3 three pictures prior to sending back the throttle body to me. In picture 1, the rebuilt throttle is completed and noticed the white label on the right that should have been green color bar code and was smeared away. In picture 2, another angle of the throttle body rebuilt. In Picture 3, old wire harness, old clutch and gear? were replaced.

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Today, the throttle body or EA arrived at my home. Inspected the rebuilt parts along with the defective parts that were replaced, the old wire harness was very fragile with open wires, torn insulation, etc. The other two defective parts including the gear and the clutch, I cannot see why they were replaced. Maybe bent, worn out, etc. Maybe the repair technician did some tests on the old clutch and gear (as shown in the pictures on this thread) and found out to be defective. I was impressed with the EA, very cleaned on top, bottom and all four sides of the EA and brand new wire harness on the EA. I am looking forward to complete the job I was set out to do in the first place.

How much did they charge for the re-build?

$203

The throttle body or EA is now on the engine. Fired up the motor and so far running good. Will be testing the EA and see if the same troubleshooting codes that was the issue in the first place is now gone. Stay tune for update results.

The latest update:

Prior to driving the Mercedes this morning, I did a DM (16 pin diagnostic module) self test. Code 6 shows up. Code 6 refers to Idle speed control faulty. That is the only code showing using the DM.

Did a code reader scan on pin 6, shows code 9, SRS malfunction indicator lamp (A1e15) or time limit for DTC readout /erasing.


Code reader scan on pin 8, one blink meaning no codes.

Code reader scan on pin 10, one blink meanng no codes.

Code reader scan on pin 14, code 2 meaning EA/CC/ISC control module (N4/1) or Safety contact switch (M16/1s1) or Stop lamp switch or Cruise control switch or Actual value potentiometer or Starter lock-out/back-up lamp switch or engine speed signal or vehicle speed signal or closed throttle position switch or safety relay in EA/CC/ISC control module.


Start up the motor and rmp shows high idling around 15000. Normal idling rpm should be around between 7000 rpm and 8000 rpm, even the same rpm when pressing the brake . Oil pressure reading between 2 and 3. On the warning lights in the instrument cluster panel shows oil sending unit on. That darn smoke (no blue smoke, just close to clear color type) out behind the engine is still there. No smoke coming out the exhaust tail pipe. Press the brake and put in drive and rpm hovering around 10000 rmp. While shifting from Park to Drive, there is a hesitation between shifts. The same results applied to reverse shift as well. Took a test drive of 25 miles or so. I put on the cruise control and it works!! Smooth driving so far, but I also smell burning smoke coming through inside the car with windows rolled up. Tried the heater on and works normally as well as the air conditioning unit. OIl pressure while drivng stayed on above 3 needle mark. Warning light on the oil sending unit stayed on, went away for awhile and came back on again. When pressing the brake to stop while driving on the road, Oil pressure hovering around between 2 and 3.

When I got home, I checked for leaking oil on the engine area and no signs of leaking oil that I can detect of. Also, I checked the oil level on the dipstick and it is fine. I did another dm test and code 6 shows up again. Testing with the code reader on pin 6, no codes. Pin 7, no codes, Pin 8, no codes, Pin 10, no codes, Pin 14, NO CODES!! YEAH, ALRIGHT!! It seems that the throttle body or EA is actually working, (after got it repaired) especially the cruise control unit, but still that darn high idling still persisted as indicated on the Diagnostic Module Self Test code 6, even though there is no codes showing on Pin 14.

Also, clear color smoke was still there along with smelling of burning oil and I was abled to pinpoint the location of the smoke area. It was on the exhaust side near the rear of the engine. There is a pipe or tubing connecting to the EGR valve. I am not sure of the exact spot of the smoke. After turning off the engine and finishing the codes test, I fired up the engine again and this time no smoke or no smell of burning oil. I will continue to monitor the smoke and the burning oil smell.

The only thing left to for me to do at this point is to find out why and fix the high idling even though the repaired throttle body or EA apparently is good, since the cruise control works and no codes showed up on Pin 14. However, on the Diagnostic Module self test shows code 6, meaning Idle speed control faulty. That does not make any sense to me. Could it be the control module (computer) behind the battery is faulty? Loose wiring somewhere? Could the high idling and the shift hesitation in drive and reverse be related? Will have to investigate and research on this and I am hoping that the Throttle body or EA is not the problem. If it turns out that the throttle body is the problem, then I am going to send the EA back to the repair shop that did the work/repaired on the throttle body. The throttle body or EA has a 3 year warranty. In addition. the light up oil sending unit needs to be fix as well. Any feedback/comments on these two issues is greatly appreciated.

I compiled a list of potential solutions to the DM code 6 (idle speed controller faulty) found on this forum and elsewhere. It is, by no means, not a complete list.

Things to check for high idling:

Try to remove the MAF sensor while the engine running and see if there is any difference and also clean the MAF sensor using MAF cleaner spray.

clean the EGR valve

Vacuum lines near and around the EA missing, loose, not airtight or cracked

Clean the purge regulator in front of engine (remove front chain cover first) The purge regulator is behind the front engine black cover

check the spring on EA and throttle rod to make sure both are intact and in good shape.


Check the RESONANCE IDLE AIR VALVE INTAKE MANIFOLD for electrical wiring connections and the vacuum line connections around the throttle body.

Just for future reference, an idle fluctuation on M104 engines is only caused by one of three problems:

1. a vacum leak

2. a faulty Mass Air Meter

3. a faulty throttle acutator, aka EA / ISC / CC module (Electronic Accelerator, Idle Speed Control, Cruise Control). Throttle Acuators go bad for two reasons. The wirirng harnesses to the throttle actuators has insulation on the wiring that flakes off. This is a problem for 1993-1995 only. Throttle Actuators also have potentioameters that wear out over time.

In some case where clearing DM (pin 3) codes require to go through the clear procedure, then turn ignition off, wait a half a minute or so, then turn igniton back on and check again. You should then get no blinks. You will not get a single blink until you have completed several drive cycles with no faults.

If you have a fluctuating idle, the first thing to check is for a vacum leak as it could be simply a hose that has come disconnected or cracked.


Someone said If the throttle body is clean, but the diagnostics says it is faulty, he still be inclined to remove the whole unit (you would normally have cleaned it from the top without removal) and clean and lube all the linkages and pivots. If it's sticky and tight it will not respond correctly, same scenario.

Another possible solution from someone who had idling issues: Changed the MAF and idle control valve (RESONANCE IDLE AIR VALVE INTAKE MANIFOLD near the throttle body (EA), also changed the fuel pressure sensor and the OVP switch. (Sorry if I had to repeat myself)


These are possible solutions mentioned above. Just throwing in my two cents' worth and hopefully help those who are having these similar issues such as mine. I will go ahead and try these steps and will report my findings. Stay tune for update.

Today latest Update:

Removed the MAF sensor and sprayed with CRC MAF cleaner. Put back the MAF sensor to its regular placement.

Ran the dm codes and still code 6 (faulty idling issue). Code reader in pin 8, no codes, pin 14, no codes.

Start the engine. At first, idling needle went up to 13000 rpm, then settled down around 8000 rpm. Pressed the brake, same results (8000 rpm). Put in drive, shifting was hesitating. The same hesitating goes in reverse as well. All shifts showed identical 8000 rpm idling at the same time pressed the brake between shifts.

Drove the Mercedes to the store. Driving was smooth, cruise control works.

Went home, turned off the engine and fired up the engine. Idling went very high around 30000 rpm. Pressed brake and shift to drive, idling went down to the normal range (8000 rpm). At the same time, oil pressure unit was hovering around the needle range of 1 and 2. Oil sending unit warning light on. When accelerating on the pedal. Oil pressure around 3. Smelled burning oil again, same location (source of burning oil is by the EGR valve tube or pipe).

Ran the code reader, same results as above, except pin 8, code 13 (O2S (Lambda) control system operating at rich or lean limit). Cleared the codes with code reader.

Next is to check the oil sending unit by the oil pan and checking the wiring as well. If necessary, I will get a new oil sending unit and to see if that would resolve the issue of oil sending unit warning light as well the floppy needle on the oil pressure unit (to stablize the oil pressure).

Also, will check the reasonance valve and throttle EA for vacuum leaks in the area. In addition, checking the wiring for cracks, frayed, etc.

If I cannot find the location and source of the oil leak near the EGR valve area while checking the oil sending unit and its wires, then I will take the Mercedes to the shop for oil leak diagnosis.

Stay tune for further updates.

Today this morning, I decided to put the CRC Mass Air Flower cleaner spray into the Purge switchover valve vacuum hose nipples. I wish I had my camera working to take some pictures which will show what I am talking about. I noticed several interesting potential issues:

Purge switchover valve missing two rubber boots with ends tops (cover tops). on right side (not the top ones) facing me. Yes, the same two hose nipples as described above.

Also, two prong female electrical connection wiring dangling by itself near the purge switchover valve. The other two prong electrical wiring is already on the bottom of the purge switchover valve. Suppose to connect somewhere. I also noticed some kind of metal housing in front right side of the purge switchover valve that the electrical connector that should be placed there?

There seems to be missing electrical connector wiring that goes somewhere near or on the purge switchover valve on the right side near the two vacuum male openings where supposedly missing two rubber boots goes into them.

The reasons I know this purge switchover valve potentially having issues is because I made a comparison check on my other 1994 Mercedes wagon (with ASR) purge switchover valve and all its connections (rubber boots, electrical wiring connectors, vacuum lines, etc.,) are intacted.

Boy, this is going to be interesting. Could this be the root of all the problems/ issues I described in my thread on my lastest/previous post? Never mind the throttle body EA repaired. The throttle body EA repaired had to be done, regardless/anyway. Will get my two ramps on to the front wheels to get a good look underneath to find the other wiring connector goes to and other possibly loose wiring and/or rubber/vacuum hoses as well. Just follow the locations of the other end of the wiring connections, vacuum lines. Also, do another comparsion check with the other 1994 E320 wagon (with ASR) as well while underneath the engine area. Nice to have another similar wagon to do a comparison check. Almost all the parts on both wagons are identical. I will not do this today due to rain and will follow up as the weather gets better. Stay tune for further updates.

Update:

For clarification, the missing electrical connector wiring refers to smog pump connector. No issues on that one.

purge switchover valve is clean and vacuum tight.

Put in CRC Mass Air flow spray into the EGR valve in front rubber nipple hose after disconnecting the metal pipe hose. Reconnected the EGR valve hose.

Cleared codes prior to driving. All codes cleared without blinking on dm button 2.

Fired up the engine. Idling around 1100 rpm. Warm up to 85c. Iding going down to 800 rpm. Pressed brake, same 800 rpm. Reverse, drive shift, same 800 rpm. Little hesitation between shifts.

Took a drive, cruise control works ok. Oil pressure hovers around between 2 and 3. Same warning lights on oil sending unit.

Stop engine. Checked the DM. Code 5 (Exhaust gas recirculation inoperative) and Code 6 (Idle speed control inoperative)


I had an extra reasonance valve intake. Did a swap of the reasonance valve intake. There are two parts to the reasonance valve intake. One is I called the flapper that goes inside the intake manifold next the throttle body. The other part is the top with the two prong male electric plugs and vacuum nipple that goes inside on the top of the flapper.

After the swap, test drive the mercedes. This time it was worse, rpm out of normal range, shifting gears long hesitation. No good.

So I took the orignal reasonance valve flapper that was performing better back on the intake manifold with the second top of the reasonance valve intake. Results were much better and less hesitation on the changing gears. It seems the top part of the original reasonance valve is faulty which was replaced by the second one. In addition, no blink codes on DM. The code reader shows no codes. Issues resolved. Thanks to everyone who read and posted comments on this thread. It had a been a long process/journey with a lot of bumps on the way. Thanks again.

P.S. I ordered the new oil sender unit, egr valve, oil pressure sensor, and fuel pressure fuel regulator. Stil have that pesky burning oil smell and smoke. That is another story.