jonUF02

Yes, I have searched all forums far and wide, I know there are a lot of these threads, but I have checked nearly everything and I don't know what this issue is.

Symptoms: rough idle when I come to a stop or in park. There have been no warning lights ever. This started about the same time as my radiator started leaking, (separation between plastic and metal secitons) and it has been replaced with Bher OEM radiator. Shaking seems to be a little worse after car is really warm, after 20 minute commute.

Troubleshooting so far:

1) Motor mounts - I know the previous owner changed them (forum jbenz99). Does not matter if car is in gear or not, does not "clunk" into gear

2) Spark plugs and wires are fairly new, replaced by previous owner. I have the car about 1.5 years now, 15K miles. I also removed all 16 spark plugs and cleaned all the carbon from them with laquer thinner and a wire brush. They are OEM Bosch 9477 plugs.

3) MAF sensor - has been cleaned, no codes, stats are stable on scanner software.

4) Took the car to the Stealership for $150 diagnositcs. They told me the cats are bad and wanted to replace both cats and all 4 O2 sensors to the total of $3400 - I said no thanks. They also found stored #6 misfire, and set my alarm to "Netherlands mode" to make it chirp!

Since the diagnosis was bad Catalytic converter, I did a lot of research on the subject. I collected data on the sensor voltages and plotted it out. The rear sensors are almost flatline when held at 2K RPM after fully warmed up. The front sensor data oscilates up and down as it should. the sensors seem to be functioning correctly, and the data does not prove to me that the cats are bad. The data plots look normal according to my research. If the cats or sensors were really bad, then I would be getting OBD2 codes, but I am not. I don't want to throw a fortune into replacing these, I don't think the diagnosis is correct.

My next suspect is possibly the EGR valve, but I don't want to just throw parts at it. Here are some other possibilities I have found, but again, I want some opinions before I throw in expensive parts. I don't have any lights or codes to guide me, just an annoying rough idle.


Water pump - it does not visibly wobble or shake the belt. I have notices a little extra noise coming from the belt/pulley area since the radiator leak.

Fuel filter - not too expensive, but not sure if this could really be the cause.

Electrical system - possible alternator or battery issue - not enough power in the system? I haven't noticed any difference in cranking power, or any change in idle when I turn on and off electrical things like stereo, lights, AC, etc.


What else could this be????? Please help with opinions.

dlbehrns

"My next suspect is possibly the EGR valve, but I don't want to just throw parts at it."
There is a thread on removal and cleaning that sounded fairly simple. Its just hard to get to.
How many miles on the car? 15K? or did you just put 15 on it?

Another thought: can you get a floor jack under the car and jack up the motor just a little bit while it is idiling rough? If the idle smooths out, there's your problem/motor and or transmission mounts. Just a SWAG(scientific wild *** guess).

jonUF02

I'm pretty confident that the mounts are not the issue. I have replaced mounts on other vehicles and I know the symptoms. It does not rattle or clunk into gear, does not matter if I'm in park or in gear. I will try the jack test though.

For the effort of removing the EGR, it's probably worth replacing. I will need to get the special star sockets for that anyway.

The car shows 126K miles, plus about 20K more because the cluster was replaced due to dead pixels. I have put 15k on it and it has been running perfectly to this point. Previous owner was a mechanic and the car is in amazing condition for the age and mileage.

cindyclk

I would replace the maf with an oem ( autohauz).......
Just double check these...make sure no vacuum leaks ....is the rear of the air filter seated properly.?( seat the cover into the maf housing first, then lower front.....)
Keep us in loop if you get to bottom of your issue.

jonUF02

I also replaced the air filters (with new K&Ns). The filter housing appears normal, I have taken it on and off many times in the process.

The MAF readings on the scanner show no trouble. and most people reporting MAF issues have various codes, I have not had any codes at all.

I took a quick look at the vacuum connections I could find. I think that warrants further investigation when I get a chance.

I have been ordering some parts from AutohauzAZ - radiator, hose, stering damper - they are good for Benz parts.

cindyclk

Don't want to start controversy but many forum members have reported maf failures w/ k&n filters...many times the maf does not throw codes...other times o2 failure/ misfire codes.
Reason for properly seating cover into maf is that you get weird airflow that screws up readings.

jonUF02

MAF readings are normal. The filters were installed after the trouble started, no change.

dlbehrns

That is what happened to my MAF w/under 20K. Went to a cold air intake and changed the MAF, wa-la. Autohausaz has a sensor replacement(minus the housing) that doesn't cost as much as the entire unit. Call to ask for it.

CurYousGee

Ive called autohausaz a few weeks ago asking for just the insert, they said they don't sell it that way? Ended up with the usual insert plus housing. AutohausAZ says the Porsche maf comes that way but not the clk? Maybe i talked to the wrong person

mfgulla77

I recently checked my EGR and found it clean but the vacuum supply
Hose was baked and cracked.

jonUF02

I'm pretty sure an MAF failure would show a code and light, or at least erratic readings on the scan tool. I went through the cleaning procedure anyway. There was no change, and never any lights. My next steps when I get some time will be:

Check for any vacuum leaks / cracked hoses, and use the jack method mentioned to check the motor mounts. If I get around to get the right star sockets, I might remove and attempt to clean the EGR valve.

It's still just a nuisance, It drives and accelerates fine, with no codes or lights, just a rough idle when I come to a stop.

Has anyone had problems like this WITHOUT warning lights / codes, or bad motor mounts?

aqeelr

I'm having a rough idle situation as well. Mine occurs weather it is in park or in gear, only noticeable at stop. I also observed that it is much more stronger on the passenger side than the driver side. So far I have changed the spark plugs and air filter. Oil levels are good too. Next step is to do the fuel filter. I've been advised to clean the MAF, I'm not sure how much that will help. I'm going to be cleaning it tomorrow after work and I'll report back if it does anything for me.

jonUF02

today I tried a couple of things:

I put the jack under the oil pan and lifted up to test the motor mounts, that is definitely not the problem. It still feels like a slight mis-fire while this was in place.

I used a can of the spray sea-foam, injected at the intake, with the tube down in past the MAF sensor. I got a nice cloud of smoke in my neighborhood when I took off the first time, but no change in idle. Actually, it was worse for a while until all the sea foam stuff was gone, now back to the same.

I'm curious if anyone has seen an issue with a cat causing this problem, but no lights / codes? I have taken many readings and they look normal according to my research. It will be a very expensive job to replace with no guarantee, but that is the dealer diagnosis.

jonUF02

I'm considering replacing the MAF just because this problem is driving me nuts. Has anyone had a bad MAF confirmed without any codes / lights?

Does anyone have a spare that they ordered only to find out that is not the problem? Want to sell to me?

Does anyone know the part number for the Bosch insert only? I found it one time, but now I can't remember where.

My scan tool is showing the MAF reading at about 5-6 g/s on idle, and steadily increases with the throttle. (in park). This seems to be normal, but I have seen some posts with other MBs where the sensor is just slightly contaminated or bad causing slow reaction or bad curve. I did the cleaning procedure, and it looks very clean all around.

jonUF02

More testing today revealed the following:

Idle with MAF connected gets a reading of 5-7 g/s from the MAF

Idle with MAF DISCONNECTED gets a reading of 9-10 g/s on my scan tool.

I am assuming there is some kind of fail-safe programming for no input from MAF sensor, and the computer thinks 9-10 g/s at idle should be correct. The shaking / misfire on idle seemed better without the MAF connected, but not 100% yet.

Can someone please take a reading at idle with a known good MAF?

Most cheap scan tools or computer programs should provide the data. I'm using a free program for this reading: DigiMoto Lite with a cheap USB to OBDII cable. I would like to have this comparison. I am now strongly considering replacing the MAF for $150 after this test. A little better may be worth the cost. Maybe the MAF is slightly failing and giving an incorrect low reading? Maybe a new MAF would resolve the issue after a the computer adapts?

jonUF02

I replaced the MAF with Bosch from Autohauz - OEM - no change in the symptoms. Readings are still 6-7 g/s from the MAF at idle. (anyone need to buy a barely used MAF?)

I got my hands on Carsoft software for Mercedes with the large round pin STAR connector. I was able to reset all engine adaptations and re-load stock configurations to the computer. After this (before new MAF) it seemed to get better, and then slowly over a couple weeks regressed to the same state as before. I am going to try this again with the new MAF, but I really don't think that was the problem.

I also bought one spare coil pack and rotated it around to each cylinder, there was no change in the idle on any cylinder. I disconnected one plug wire just to see what happens, and it really changed nothing. I was surprised at that.

Next step is to install new fuel filter, already in the mail. I can see that the filter on there is Bosch, and has hose clamps rather than the original Mann with crimped connectors, but no idea how long ago it was changed.

GatorMB

Its really easy to get lost inside the box so to speak,
Going back to basics on a misfire are, Compression, Fuel, and Fire.

Fuel might be the easiest to detect by un-plugging 1 injector at a time to isolate the problem cyl. Next perform a compression test on each cyl. While you are there change the plugs for known good ones. (clean and regap is maintenance from the 60's) never a fix.

Some diagnostics software will give a static compression test to be used as an aid in locating the bad cyl.
Hope this helps a little,
Cheers, Gator

jonUF02

I don't think spark is the issue now. I knew the plugs and wires were relatively new, and the correct OEM type, so I cleaned them for good measure. I verified there was no change by swapping the coil packs. I don't really think it's necessary to spend $100 on 16 new plugs. I'm moving on to fuel now with the fuel filter. I may try unplugging the injectors as you say for further troubleshooting. I don't have a compression tester, but that may be in the future, as well as a fuel pressure tester. I still don't believe the dealer is right about their diagnosis of the CATs.

jonUF02

Update:

A couple days ago, my top idler pulley shattered (made of plastic!!!) and the belt came off disabling the car. After the car was shamefully towed home, I installed a new idler pulley, tensioner assembly (because I could hear the bearings going bad), and serpentine belt. All of this on the belt area is working fine, but the rough idle problem has suddenly gotten worse after slowly getting better over the past few weeks. Now the car will die if I sit at a light too long. Other things I have done in the process:

Replaced crank position sensor today - no change

Removed EGR valve and tube, cleaned all the gunk out, changed the vacuum hose, as well as a few other visible vacuum hoses around the top of the engine, and replaced all the top crankcase breather hoses that were brittle and broke apart.

Now I think I may have found the root cause!

While doing the work above and then not seeing any change, I spent some time listening to all the noises. I found that the throttle body is making a high pitched whine noise when the key is on, but the engine has not started. The noise is constant, and can also be heard while the engine is running if you get close enough. I removed the electrical connection to the TB while it was doing this with the key on and the noise stopped.

I think my next step will be to get a used TB and replace. Used is about $25-75 depending on the source; junk yard or Ebay. New is about $400 I believe, so I'm willing to try used and see if the noise goes away. I will update in a couple of days when it's done. Has anyone else had problems with Throttle Body like this?

jonUF02

New (salvage) throttle body is installed. I made sure to clean it nice and shiny before installation. This has definitely cured the stalling issue. The old one had a lot of crusted up carbon and oil junk on the butterfly that was probably choking it out. Funny thing is that the noise is still there. I had to clear my adaptations with the Carsoft again, and now it idles without dying, and acceleration seems to be more responsive.

Now I am back to the original idle issue. It feels like a small miss when cold, barely noticeable, and after a 20 minute commute it turns into a shake when I stop at lights. Cruising speed feels fine, acceleration is good, used to be a slight hesitation before the TB was swapped. Only problem is the rough idle.

Mounts have been ruled out, definitely an engine issue.
MAF - replaced with new Bosch
Crank Position Sensor - replaced
fuel filter - replaced
EGR - thoroughly cleaned, new gasket, new vacuum hose
Crankcase breather tubes - replaced
most vacuum hoses replaced
Throttle body replaced with reconditioned used part, all adaptations cleared (second time).
Serpentine belt, idler pulley, and tensioner replaced. All pulleys checked for visible or audible issues.

My next action will be to replace all 16 spark plugs with new ones, Bosch 7422 OEM plugs, and check compression in the process. I have ruled out the coil packs by swapping one new (used OEM) pack to each cylinder in rotation with no changes. The wires look very new, and are Bosch. I also grabbed the camshaft position sensor out of the salvage car, and I will try swapping that as well.

GatorMB

Hey Jon,

Sounds like your right on top of it so to speak,
I limped my CLK home and the first service was oil change, plugs and wires.
Found it easiest to remove the coil packs with the wires and assemble them on the bench, Coil side connections are snap lock, also look for cracks in the coil packs.
I applied silicon sealer to Band-Aid it until one fails.

All the Best, Gator

jonUF02

I may have resolved the idling problem!

I bought a kit to rebuild my fuel injectors; new o-rings, retainers, and little filters for the top. Less than $25 for the kit for all 8 injectors.

I removed the rail and injectors. Removing the little filters was a pain, but got them out with a small screwdriver, cleaned everything with carb cleaner, and put everything back together. I failed to do any testing before re-assembly. I started the car and it was terrible. I removed everything again and did some testing using procedures I found on Youtube that can be done with some common household items:


I found I had 2 bad injectors. 1 was stuck open, did not hold pressure, and did not click when power was applied. 1 would click over, but did not hold pressure. I don't know if they were bad when I removed them, or if it was a possible result of my work in the rebuild process, but definitely bad now, and flooding the cylinders, not holding fuel pressure.

I got 2 injectors from a parts car, cleaned them up thoroughly and tested them as good. I put everything back together again, and now the idle seems to be resolved about 99%. I still feel a tiny shake some times, but for the most part is is purring again. I will see how it shakes out over the next few days.

I still plan to change out the spark plugs and test the compression when I get some time.

I should also add that I replaced the entire exhaust system and cats from a parts car with only 46K on it. I got a deal, so I thought it was worth ruling out the exhaust / cats that the dealer told me was the issue. WRONG! There was no change with the new exhaust. I may offer the old one for sale if anyone wants it, obviously nothing wrong with it.

GatorMB

Hey Jon,

That's what I call going the extra mile on fixing it right.

Some other notes on compression testing: Static readings can be accomplished without the actual tester, although removing a plug and getting the actual reading with the proper gage is best.

RPM drop test: 2 ways to accomplish with a high resolution tach (mechanics tuning).
disconnect one injector plug at a time and note differences in idle RPM. The other is with a vacuum gage (non damped) installed and note any needle fluctuation @ idle while performing these tests.
The ECM will pick up the lost cylinder during this test quickly so you will have to absorb notes quick as well.
Some ECM diagnostics software has a static cylinder reading built in for problem sessions like yours.

Thanks for sharing the injector info!!

Gator

jonUF02

Injectors were not the fix, still having the shakes. FML... more troubleshooting.

MarcusF

I've changed my motor mounts twice. They are a normal wear item and based on the bizarre 113 firing order, I'm surprised they work as well as they do. If nothing else, you may want to pull them and do a visual inspection. It's a straightforward job that can be done in a couple of hours. I had one that looked good until it was on the garage floor, where I could see it was bad.

If it's not the mounts, you may want to pull the MAF and check the rubber seal under it.