frustrated, hopefully someone can chime in:

started having rough idle issues a month ago and with 100k miles on my clk55, figured it was time for a major tune up. I had most done at a merc indy:

16 oem bosch spark splugs
16 oem bosch spark plug wires
two oem engine mounts
maf sensor from autohausaz
all fluids flushed/drained/filled
oem air filter
oem fuel filter
replaced valve cover gaskets
replaced engine belt

he reset the adaptation figures and i drove it 200 miles and still same issue...these are things we have done:

replaced 16 spark plugs again
replaced 16 spark plugs wires again
recheck engine mounts

started digging some more and monitored the cylinders and found that cyl 4 was behaving a bit weird...not sure the terminology but if at idle it's suppose to be 1.0, cyl 4 was fluctuating between -1 and 4.5...we swapped coil packs...still only cyl 4 had issues....could it be fuel injector? i only use premium 93, usually shell, but on occasion hess or mobile...i've used techron once and doing it again...

again started digging and started monitoring the o2 sensors...upstream o2 sensors were very erratic...spikes were all over the place....soon it will need to be replaced...could an o2 sensor wreck havoc on a cyclinder?

could it possibly be tranny mount? i can see the engine shake at idle...it looks like it's shivering...

i have no cel, no stored codes, and acceleration is still great for 100k mile engine, although at times when i punch it, there's a slight hesitation/choke...

it would make life so much easier if there was a check engine light or stored codes...i have nothing...ecu thinks its perfectly normal that i have a rumbling 5.5 liter old school muscle car

 

O2 sensors are used while in closed loop mode. Idle is controlled by close loop. If the O2 sensors are original, at a minimum I’d change the upstream sensors.

 

O2 SENSORS FLIP FLOP FROM 0 TO 1.O RANGE WHEN OPERATING NORMALLY, YOU MAY SEE .25 TO .80 OR SOMETHING SIMILAR IN RAPID SEQUENCES, NORMAL. TROUBLE WHEN THEY START GETTING CONSISTENTLY LEAN OR RICH IN CLOSED LOOP, [READING CONSISTENTLY ON ONE SIDE OF .475 OR .500 ] BEWARE OF OPEN LOOP [COLD] READINGS OF .475-.480, THEY MAY BE ECM GENERATED DEFAULTS UNTIL SENSORS GET HOT.

 

thanks for the advice...think the o2s might be the culprit...we watched the graph while cold and revved and waited until warm/hot...it was still very lazy/erratic...it spikes then flat lines for a few seconds, spikes a little, flatlines for a sec, then never reaches the original base line...

 

good news and bad news...replaced both upstream o2 sensors and idle got better...issue is during cold start or when parked, the engine shakes...when warm and in drive, engine is smooth as butter...

could the rear o2 sensors cause cold start/in park engine rough idle? could fuel injector cause an issue? still no malfunction codes...

 

The rear sensors are used to monitor the cats. They don't impact A:F ratios. Some ROW cars don't have the rear set - see WiLL's photos from Japan.

 

hmm i'm at a lost as no one seems to be able to figure this one out...i guess next step would be to test the fuel injectors? for spray pattern?

 

cked for vacuum leaks yet? pull the air box and try metering the airflow at intake with your hand. Things smooth out and you know your looking for a leak. Idle drops then you know your tight... just a thought

 

just tried covering the air intake with a cloth and hand and engine still shakes...haven't gone through smoke testing for vacuum leak yet...

idle needle doesn't fluctuate, just can feel and see the engine shake...but if in drive, the idle is smooth and engine doesn't shake....only in park....could somehow the initial idle be too low? my idle is about 500-600...

 

if you cant change the idle with your hand over the intake you dont have a leak so I wouldnt look further that way. Idle sounds bout right.. least thats bout where mine is???

 

the engine shake is normal, and being transferred to the chassis because of failed motor mounts

~mike~

 

already changed motor mounts...although transmission mount wasnt changed...

another theory is the crank position sensor...could be on its way out since it measures the fuel/air ratios when cranking?

 

The CPS checks the crank position/engine speed. Also, air fuel ratios are not checked while cranking.

 

Common symptoms of CPS going are 'starts when cold but not when hot'.

I too would say motor mounts if you hadn't already changed them.

 

we have changed the motor mounts, i'll double check and make sure it wasn't defective from factory new...

 

Just had a thought.. you said you put in new mounts so they will be fully expanded allowing maximum insulation. How much vibration you talkin?? I mean a failed mount will make the idle appear smoother to the eye but youll feel it in the body. The opposite applies to fresh mounts in the they are designed to let the motor move around while NOT transmitting the vibration to the body. Starting to sound like you may be chasing a ghost??

 

At this point, I have just about replaced everything and I can feel the car shake when in park....in drive and stopped, I can feel a bit on the seats....it got significantly better when I replaced the upstream o2 sensors...the downstreams are next...then its off to smoke testing for vacuum leaks..

 

You may want to take a close look at your vibration damper / main pulley. I've read about them coming apart on some cars, but I thought it only impacted the 2000 and earlier engines (ME 2.0).

The 430 damper is $63 (list price is $84). The AMG part is a little bit more money - $278 ($370 is the list price). Some part searches show the 55 using the same part as the 430, but I think they're wrong. MB of Annapolis says they are definitely two different parts. You may want to buy a new bolt too. On many cars that's a stretch bolt.

 

I checked with mb on the recall and my vin doesn't fall within the recall vins for the crank pulley....when I had the mechanic replace the engine belts he double checked for cracks and abnormalities...I could have him double check and if defective, can upgrade to ams crank pulley...

 

I also have the exact same problem with my 2002 CLK 320. Any success with the downstream 02 sensors? I have replaced both motor mounts but like you did not replace the transmission mount. Couldn't imagine it would be that much of an issue but could be wrong.

 

still have the same issue...my mechanic will be looking into the w209 engine mounts and also do the transmission mounts this friday...will report back if it solved the issue...

timothy: i didn't do the downstream o2 sensors because when we plugged the star diagnostic software in we didn't see any issues with any parameters...

 

changing to w209 engine mounts and a new transmission mount didn't solve my issue

after replacing just about everything, i've narrowed it down to trembling when idle at park only....idle in drive or neutral or reverse is smooth...under load its smooth as butter...

i'm thinking it's either fuel injector line is dirty or has water or the rear O2 sensors are creating a havoc on the trembling engine...

so odd that it only trembles when the engine is NOT under load...any ideas?

 

bump for any ideas

 

have you thought about taking it to a dealer? i know lots of people call them "stealerships" but bottom line, no one knows your car better. when i used to work at a dealership, many times we could diagnose a problem on the spot, just by listening to the customer explain the symptoms...we had seen the same issues over and over.

dealers may be more expensive, but usually they will try really hard to make you happy. they all live and die by customer satisfaction these days....and if you add up all the money you've already thrown at the problem, would probably be cheaper.

i too use a european indy for most things, but this kind of trouble shooting, electrical issues, conv top adjustments, i take to the dealer. worth the extra money in my mind. just my .02

 

thanks for the tip aqua but two different dealerships just said deal with it, the vibration is minor compared to the 63 motors...

i'm guessing since my car is old, they don't really want to deal with it...keeps telling me to trade up if i'm not happy with the idle....