Erratic Idle M112 Engine
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2005 C240, 2001 ML320
Erratic Idle M112 Engine-- SOLVED!!
I have been chasing a rough idle issue on my wife's 2005 C240 Wagon which we have owned for about 6 months.
I have done a TON of searching on this issue (which seems to be all too common) and have replaces a few of the parts which are due on the car as it has close to 100k miles
So far I have:
1. Re-sealed the the valve cover breathers
2. Replace the Valve Cover Gaskets
3. Replaced the Spark Plugs
4. Cleaned the MAF
5. Cleaned the Throttle body and Elbow
6. Checked the EGR Tube (it was clean)
7. Replaced the seals around the MAF and TB
8. Replaced the breather hoses which go to the valve covers
9. Replaced the spark plug wires
10. Replaced the Air Filters
11. Checked engine mounts (they are are good)
Still the idle is off. Almost sounds like a miss, but there are no codes.
I have a code reader which can read live data and here is what I see.
Engine speed is erratic... goes between 677-812 RPM.
Engine spark advance is also erratic... goes between -9 to +6.5
I also have a 2001 ML320 with the same basic engine. This idles smooooooth. RPM goes between 678-724RPM. Ignition timing is MUCH different at -20.5 to -16.
So here is my question... what controls the idle on these engines? I know it's the ECU, but what inputs are used?
Anyone have any ideas what else I should check?
I have done a TON of searching on this issue (which seems to be all too common) and have replaces a few of the parts which are due on the car as it has close to 100k miles
So far I have:
1. Re-sealed the the valve cover breathers
2. Replace the Valve Cover Gaskets
3. Replaced the Spark Plugs
4. Cleaned the MAF
5. Cleaned the Throttle body and Elbow
6. Checked the EGR Tube (it was clean)
7. Replaced the seals around the MAF and TB
8. Replaced the breather hoses which go to the valve covers
9. Replaced the spark plug wires
10. Replaced the Air Filters
11. Checked engine mounts (they are are good)
Still the idle is off. Almost sounds like a miss, but there are no codes.
I have a code reader which can read live data and here is what I see.
Engine speed is erratic... goes between 677-812 RPM.
Engine spark advance is also erratic... goes between -9 to +6.5
I also have a 2001 ML320 with the same basic engine. This idles smooooooth. RPM goes between 678-724RPM. Ignition timing is MUCH different at -20.5 to -16.
So here is my question... what controls the idle on these engines? I know it's the ECU, but what inputs are used?
Anyone have any ideas what else I should check?
Last edited by ordway.dc; Apr 13, 2014 at 03:47 PM. Reason: added Solved to Title
Thread Starter
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2005 C240, 2001 ML320
Along those lines I am on my second bottle of injector cleaner and am planning a third on my next fill up. Funny thing... I never had my injectors cleaned on my 01 ml320 and it runs great.
Also, something I forgot to mention
12. Checked fuel pressure. 55 psi on the dot.
Any ideas how to narrow this down to a sensor or something? I'm thinking about checking the Crank position sensor. I know this failing/failed causes a no-start, but maybe it's loose?
Also, what does the cam position sensor do? Could this be going bad?
Also, something I forgot to mention
12. Checked fuel pressure. 55 psi on the dot.
Any ideas how to narrow this down to a sensor or something? I'm thinking about checking the Crank position sensor. I know this failing/failed causes a no-start, but maybe it's loose?
Also, what does the cam position sensor do? Could this be going bad?
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2005 C240, 2001 ML320
There are 4 seals in the MAF/TB/Elbow area and I replaced them all.
I can't hear a leak in that area. I am sure the parts are all seated properly. I can see that using a mirror.
Today I am going to take off the serpentine belt and see if it idles more smoothly without accessory load.
I can't hear a leak in that area. I am sure the parts are all seated properly. I can see that using a mirror.
Today I am going to take off the serpentine belt and see if it idles more smoothly without accessory load.
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2005 C240, 2001 ML320
Checked again without the serpentine belt installed and it ran the same. All pulleys spun well.
I'm starting to wonder if the PO got MAF'd with an Audi/VW MAF. I need to check the numbers on it to be sure.
This MAF says my engine is using about 5.5 g/s of air at idle. I think others have reported something like 3.1, but I need to double check that.
I'm starting to wonder if the PO got MAF'd with an Audi/VW MAF. I need to check the numbers on it to be sure.
This MAF says my engine is using about 5.5 g/s of air at idle. I think others have reported something like 3.1, but I need to double check that.
Last edited by ordway.dc; Mar 30, 2014 at 01:23 PM. Reason: added MAF reading info
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From: Reston VA
2002 C240 Auto 85K
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2005 C240, 2001 ML320
Yes, The ML uses the same MAF. I thought about swapping them, but its too late today.
I did unplug the MAF and the idle got worse. Also, if I pressed the gas pedal down, it bogged down and seemed like it would stall.
I did some other things to the car today. I checked for vacuum leaks by putting 2-3 psi on the intake and covering the MAF with a latex glove. There was a slight leak but I couldn't tell where it was coming from. Anyway, I tore apart the MAF down to the TB. I disassembled the TB and did the cleaning in the link tikara just posted (I saw this before) and reassembled everything. Checked for leaks again and had none.
Overall the car seems to be running better. But the rough idle is still there, just less pronounced. Idle is now between 680 and 742. The ignition timing has also settled down a bit, though not as much at -9 to +1.5.
I am planning to run another tank of gas with Techtron Injector cleaner. I'll try a MAF swap, too.
I did unplug the MAF and the idle got worse. Also, if I pressed the gas pedal down, it bogged down and seemed like it would stall.
I did some other things to the car today. I checked for vacuum leaks by putting 2-3 psi on the intake and covering the MAF with a latex glove. There was a slight leak but I couldn't tell where it was coming from. Anyway, I tore apart the MAF down to the TB. I disassembled the TB and did the cleaning in the link tikara just posted (I saw this before) and reassembled everything. Checked for leaks again and had none.
Overall the car seems to be running better. But the rough idle is still there, just less pronounced. Idle is now between 680 and 742. The ignition timing has also settled down a bit, though not as much at -9 to +1.5.
I am planning to run another tank of gas with Techtron Injector cleaner. I'll try a MAF swap, too.
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From: Orange County
2005 C Wagon (No snickering please!)
With the timing jumping around at idle methinks it might be a crankshaft position sensor. It did not hurt that you cleaned the resistance tracks on the throttle body, and you should consider a new fuel filter if it has not been changed at 100K. If it has been changed with one other than OEM or OE manufacturer, that might be your problem. The regulators in some aftermarket units are not effective.
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2005 C240, 2001 ML320
I purchased a fuel filter (Wix Brand) but have not installed it yet. I was thinking about installing it and cleaning the fuel injectors at the same time. Too tired tonight to do this though... maybe tomorrow.
BTW, I always buy Wix or Mann filters and have had good luck with both brands.
Funny thing... I just looked in the box for my fuel filter and the part has "Mann" printed on it.
Another funny thing. I also bought a CPS, but the day before it arrived the CPS in the ML gave up the ghost. So I had the install it in the ML. Another one is on the way now.
BTW, I always buy Wix or Mann filters and have had good luck with both brands.
Funny thing... I just looked in the box for my fuel filter and the part has "Mann" printed on it.
Another funny thing. I also bought a CPS, but the day before it arrived the CPS in the ML gave up the ghost. So I had the install it in the ML. Another one is on the way now.
Last edited by ordway.dc; Mar 31, 2014 at 10:51 PM.
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C240 4MATIC
I'd try a new MAF. When mine was going out, it didn't show any codes or anything. The indy shop couldn't even figure it out. I had to do it myself. Everything improved once I put in the new MAF. But now I'm having another idle issue 
I believe I need a new voltage regulator for my alternator since all the electronics flickers @ Idle.
I believe I need a new voltage regulator for my alternator since all the electronics flickers @ Idle.
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2005 C240, 2001 ML320
Well I replaced the Crankshaft Position Sensor... No Change.
Replaced the Fuel Filter... No Change.
I say no change, but the care is running better. It's just the idle which has not improved.
Also, changing the CPK sensor only took 30 minutes. It helps that I did the same repair on my ML320. Anyway I posted pics in this thread:https://mbworld.org/forums/c-class-w...ml#post5999176
I am going to try swapping MAF's with the ML now. I'll keep you posted.
Replaced the Fuel Filter... No Change.
I say no change, but the care is running better. It's just the idle which has not improved.
Also, changing the CPK sensor only took 30 minutes. It helps that I did the same repair on my ML320. Anyway I posted pics in this thread:https://mbworld.org/forums/c-class-w...ml#post5999176
I am going to try swapping MAF's with the ML now. I'll keep you posted.
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2005 C240, 2001 ML320
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2005 C240, 2001 ML320
In case people are wondering... The reason I did not take my car to a professional is that nearly everything I've done is normal maintenance. There seem to be a lot of problems with idle on the C240, and most of them end like this thread: https://mbworld.org/forums/4545938-post1.html
Also, I want to bring this thread to a conclusion in case it helps someone else in the future.
Also, I want to bring this thread to a conclusion in case it helps someone else in the future.
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2005 C240, 2001 ML320
Some success
So I made some BIG progress tonight. I started suspecting the EGR Valve. I removed the hose labelled b in this photo:
Then I connected a gauge to the Transducer Y31/1, and a vacuum pump (mityvac) to the Vacuum Reservoir 89/2.
With no vacuum applied by the mityvac to 89/2, the car ran GREAT.
If I applied vacuum with the mityvac to 89/2, the car ran like crap.
If I reconnected the hose between 89/2 and Y31/1, the car ran the same as my video (crap)
So for now I have plugged the line at the Y31/1 while I poke around some more. Thinking I may need a new EGR Valve.
I may get a CEL, but not so far.
Then I connected a gauge to the Transducer Y31/1, and a vacuum pump (mityvac) to the Vacuum Reservoir 89/2.
With no vacuum applied by the mityvac to 89/2, the car ran GREAT.
If I applied vacuum with the mityvac to 89/2, the car ran like crap.
If I reconnected the hose between 89/2 and Y31/1, the car ran the same as my video (crap)
So for now I have plugged the line at the Y31/1 while I poke around some more. Thinking I may need a new EGR Valve.
I may get a CEL, but not so far.
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2005 C240, 2001 ML320
I have poked around with the egr valve and I have to say I am stumped. So if you have any insight, I'm all ears.
I have checked the voltage on the EGR connector, and I read 10.8v dc when the car is cold/idling. The vacuum coming from the valve is 159 millibar, whether the electrical plug is attached or not. Also I can see the vacuum actuator pulling in if I connect hose b. As soon as that happens, the idle goes to crap.
I know the egr tube is clean. Does this scenario sound like i need a new EGR? Or is the signal wrong? 10.8v sounds a little low. Also, I thought this was supposed to be a 10Hz signal, not DC.
I have checked the voltage on the EGR connector, and I read 10.8v dc when the car is cold/idling. The vacuum coming from the valve is 159 millibar, whether the electrical plug is attached or not. Also I can see the vacuum actuator pulling in if I connect hose b. As soon as that happens, the idle goes to crap.
I know the egr tube is clean. Does this scenario sound like i need a new EGR? Or is the signal wrong? 10.8v sounds a little low. Also, I thought this was supposed to be a 10Hz signal, not DC.
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C230 2003
TIKARA suggestion.
The rough idle I've been experiencing is only happening from a cold start. It goes away as the car warms up. Today I completed doing the quick fix that the poster TIKARA posted above. My throttle body was really filthy on the side that faces the engine. The portion of the throttle body that houses the electrical component was actually really clean and I probably didn't need to do that step but I wanted to try anything that could help.
Last edited by 2subway; Apr 13, 2014 at 08:47 AM.
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2005 C240, 2001 ML320
This problem has been solved.
I purchased a new EGR valve and found that it does not allow vacuum across the valve with no power on the plug. So I installed the new EGR valve, cleared the codes, and all is well.
In addition I have a clean MAF, Clean TB, New Breather Hoses, New MAF Seals, and a New Crank Position sensor. Should be good for a while now!
In all, I don't think I spent a lot solving this. Most of the stuff I did would be considered extended maintenance. In other words, all of that stuff needs replacing when your car is approaching 100K miles as mine is.
Also, I wanted to thank everyone who helped me solve this problem; especially tikara, samaritrey, moviela, quadcammer, blzdout, and 2subway.
I purchased a new EGR valve and found that it does not allow vacuum across the valve with no power on the plug. So I installed the new EGR valve, cleared the codes, and all is well.
In addition I have a clean MAF, Clean TB, New Breather Hoses, New MAF Seals, and a New Crank Position sensor. Should be good for a while now!
In all, I don't think I spent a lot solving this. Most of the stuff I did would be considered extended maintenance. In other words, all of that stuff needs replacing when your car is approaching 100K miles as mine is.
Also, I wanted to thank everyone who helped me solve this problem; especially tikara, samaritrey, moviela, quadcammer, blzdout, and 2subway.
Last edited by ordway.dc; Apr 13, 2014 at 03:56 PM.
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2005 C240, 2001 ML320
In my case, the EGR actuator worked fine, it was just that the tan colored valve on the side of the EGR never closed. You can check this on your car by looking at the vacuum actuator and see if the actuator moves when you start the car. It shouldn't.
In order to see this you need to remove the engine cover/airbox.
While I was waiting for my EGR to arrive I simply removed the hose between the valve and the actuator and fashioned a plug from the end of a nerf dart. Car ran great but it threw a P0400 code CEL.
So you can do a quick test to see if the EGR is creating the rough idle.
In order to see this you need to remove the engine cover/airbox.
While I was waiting for my EGR to arrive I simply removed the hose between the valve and the actuator and fashioned a plug from the end of a nerf dart. Car ran great but it threw a P0400 code CEL.
So you can do a quick test to see if the EGR is creating the rough idle.
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W203 C320 & C230k, E36/E46/E90 darksiders
This problem has been solved.
I purchased a new EGR valve and found that it does not allow vacuum across the valve with no power on the plug. So I installed the new EGR valve, cleared the codes, and all is well.
In addition I have a clean MAF, Clean TB, New Breather Hoses, New MAF Seals, and a New Crank Position sensor. Should be good for a while now!
In all, I don't think I spent a lot solving this. Most of the stuff I did would be considered extended maintenance. In other words, all of that stuff needs replacing when your car is approaching 100K miles as mine is.
Also, I wanted to thank everyone who helped me solve this problem; especially tikara, samaritrey, moviela, quadcammer, blzdout, and 2subway.
I purchased a new EGR valve and found that it does not allow vacuum across the valve with no power on the plug. So I installed the new EGR valve, cleared the codes, and all is well.
In addition I have a clean MAF, Clean TB, New Breather Hoses, New MAF Seals, and a New Crank Position sensor. Should be good for a while now!
In all, I don't think I spent a lot solving this. Most of the stuff I did would be considered extended maintenance. In other words, all of that stuff needs replacing when your car is approaching 100K miles as mine is.
Also, I wanted to thank everyone who helped me solve this problem; especially tikara, samaritrey, moviela, quadcammer, blzdout, and 2subway.
