three years rough idle sl320 r129 v6 m112

[Darragh1]

my car - sl320 R1290642F177672 Gearbox 722.6 Engine M112943
I have a constant rough idle whether in P, R or N with a bit of surging when aircon is on or steering wheel in motion, i get a light massage felt through my seat when stopped in traffic - i am very sick of it

work that has been done -
removed and cleaned throttle body and egr valve/pipes
breather hoses from valve covers to maf replaced
maf replaced
air filters
oil/oil filter
spark plugs
HT leads
Engine mounts front and gearbox mount
egr lines checked
no vacum lines even cracked
crank position sensor replaced
engine very clean
put a couple of fuel treatments through the fuel tank
fuel filter
No codes when plugged in to the 38pin proper star? machine
the vibration is only when the idle is between 560rpms and 1000rpms and once the accelerator is touched it smooths out completely and drives beautifully without hesitation


I am very tired of looking into the engine with the air filter cover off and watching it vibrate, then perfectly smooth when revs touch on 1000rpm


Thank you for listening to me and if you have any wisdom to offer i would greatly appreciate it

kindliest regardations,
Darragh.

 

[kwakdonut]

Suggestions -

Head gasket (are you losing coolant/oil at all?)
Compression test?
Ignition coils?
Have you taken plugs out and checked condition of each?

 

[Darragh1]

Hi kwakdonut,

Thank you for the response.

Not losing coolant or oil.

If compression test is when the nice man plugs in the magic star machine and it shows the cylinders firing, this has been done a few times and there is no problem with the cylinders.

When the old plugs were taken out they were evenly and sufficiently greyed and the mechanic said they looked as they should.

Coils - i swapped around the coils a bit, i replaced the coil that seemed to make slightly less difference than the others when i unplugged its electrical connection with a spare second hand coil i have and nothing changed.

When the engine is idling there is no vibration visible on the rev. counter, maybe the odd tiny one but only a mm either way.

When I touch the accelerator when in P the visual vibration of the engine smooths completely. The car drives perfectly smoothly. Once stopped in PDR and N the vibration is constant until 1000rpms.

I am only learning but am capable of things like egr cleaning and changing sparks and I forgot to mention I replaced the valve cover gaskets.

Regards,
Darragh.

 

[BlackC55]

It won't be a head gasket. They never ever go on 112 engines.

I would be looking at coil packs or an injector issue firstly. The coils can be checked with a scope easily. I would do this first to see if the patterns are good to see if you have a secondry ignition issue..

Was a physical compression test done? Do you drive the car hard? Are the CATS and lambda sensors ok?

 

[Darragh1]

Hi BlackC55,

Thank you for the response.

I don't know if a physical compression test was done or not, however I doubt it.
I drive the car 2hours a day town and a bit of motorway up to about 80mph, i enjoy kickback but don't tear the car up at all.

My right cat is making that faint light broken porcelain sound on and off,mostly not at all, it has been like that since I got the car 3 years ago - is cat rattle a result of and not a root cause? O2 sensors show no fault codes. No codes at all.

Is a scope a stethoscope?-give instructions please..
If i touch the top part of the 6 injectors with my fingers i can feel their steady pulse alright.

Basic Questions due to basic lack of knowledge -
1.If it was a vacum leak of some sort, why wouldn't it affect the car while driving since it smooths once it hits 1000rpm?
2.If it is electrical (eg.coils) why wouldn't it affect the car while driving since it smooths once it hits 1000rpm?


Regards
Darragh

 

[BlackC55]

Hi BlackC55,

Thank you for the response.

I don't know if a physical compression test was done or not, however I doubt it.
I drive the car 2hours a day town and a bit of motorway up to about 80mph, i enjoy kickback but don't tear the car up at all.

My right cat is making that faint light broken porcelain sound on and off,mostly not at all, it has been like that since I got the car 3 years ago - is cat rattle a result of and not a root cause? O2 sensors show no fault codes. No codes at all.

Is a scope a stethoscope?-give instructions please..
If i touch the top part of the 6 injectors with my fingers i can feel their steady pulse alright.

Basic Questions due to basic lack of knowledge -
1.If it was a vacum leak of some sort, why wouldn't it affect the car while driving since it smooths once it hits 1000rpm?
2.If it is electrical (eg.coils) why wouldn't it affect the car while driving since it smooths once it hits 1000rpm?


Regards
Darragh

Hi,

This in BOLD is not good.

The ceramic particles in the cat when broken up can enter the engine's cylinder when the engine is switched off. This ceramic an wear the bores away over a period of time. Get the CAT fixed and a compression test done.

A scope is an oscilliscope (spelt incorrectly) that can measure wave form.

It has a mild misfire, that is why you can't feel it at 1000RPM. Its is a fair size engine the increase in RPM will smooth out any misfire so it appears not apparent.

I doubt a vac leak as ther are no other symptoms.

 

[Darragh1]

BlackC55,
I have aftermarket cats (walker)- for both sides of the car - should i install both or just the rattling one?
Do you think the rattling cat has done major damage when you say
'not good' or is it just something that needs to be tended to asap?
I will get a compression test done soon.
I work at a school - is an oscilliscope the type of thing carried by physics teachers?

Regards and thanks
DArragh.

 

[sebastianforbes]

may i suggest the dizzy caps and rotors ?

the cat issue may be as a result of unburnt fuel because not all cylinders are firing ?

this was the problem with my 500SL !

 

[jaymanek]

His car has coil packs so no caps and rotors.

Id only change the one.

 

[MB Novice]

Vibration

Darragh

I have the same problem as you in my SL280.
Have you found an answer yet?

Patrick

 

[jonathanc]

It sounds like you have exhausted all the obvious things, it is moving into the specialist knowledge area. Using a scope if no good unless you know what the waveform should be - I would really suggest that you get the car to a good indie - Olly (BlackC55) is highly recommended by forum members that have used him. It may cost a bit but he will sort it out once and for all. If you are not close to Portsmouth there are other indies on these forums that also have very good reputations.

The CAT could damage the engine in a fairly terminal way if particles of broken ceramic get into the engine, I would change it straight away.

 

[MBAussie]

Hi DArragh, did you ever fix the idle issue on your vehicle? I'm experiencing the same problem with my SL320 and it seems to have identical symptoms to yours.

 

[rorf]

Hi DArragh, did you ever fix the idle issue on your vehicle? I'm experiencing the same problem with my SL320 and it seems to have identical symptoms to yours.

BUMP BUMP:bannana:

 

[IanA2]

BUMP BUMP:bannana:

See last activity date: http://www.mbclub.co.uk/forums/members/darragh1.html

 

[Darragh1]

?i,
same problem persists.....
I borrowed a good coil and swapped it in to all 6 cylinders and there was no change in the roughness.
I have had several mechanics check for codes and nothing appears.
Harmonic balancer/belt/belt tensioner/pulley all replaced - no difference.
Just to repeat - also all servicing done air/fuel/oil filters etc plugs ht leads done / throttle body cleaned/ many air hoses replaced/ cps/ everything clean..... engine running a bit rich - a little too much white smoke form exhaust.

I got an Infra-red thermometer - when I point it to where the engine meets the exhaust manifold at each cylinder I get varied temperatures....
Maybe this is of no consequence but what do you think?
After a 30 or 40minute drives,parked - on 3different days I got the following:
Cylinder Day 1 Day 2 Day 3
1 184 196 100
2 136 186 160
3 108 132 204
4 186 202 170
5 152 189 109
6 124 186 167


Relevant or telling in some way?

Thank you for listening
Darragh

 

[grober]

If it's RPM related it could be transmitted resonant vibration. Sometimes an engine can be too tied down needs to move a bit- Could be the wrong engine mountings- location or type- don't know if they are " sided" like some of the diesels are? Could be the exhaust mountings are out of alignment/ not free to move------- Other possibility is propshaft related- either the flexible joints or the central bearing/mounting.

 

[Sp!ke]

Re-reading the original first post, the issue was only at idle.

This being the case, on yours, I would consider changing engine and gearbox mounts as they are reasonably cheap and easy to replace and on a car of this vintage will likely smooth out a lot of rattles and vibration.

 

[Chalpkin]

?i,
same problem persists.....
I borrowed a good coil and swapped it in to all 6 cylinders and there was no change in the roughness.
I have had several mechanics check for codes and nothing appears.
Harmonic balancer/belt/belt tensioner/pulley all replaced - no difference.
Just to repeat - also all servicing done air/fuel/oil filters etc plugs ht leads done / throttle body cleaned/ many air hoses replaced/ cps/ everything clean..... engine running a bit rich - a little too much white smoke form exhaust.

I got an Infra-red thermometer - when I point it to where the engine meets the exhaust manifold at each cylinder I get varied temperatures....
Maybe this is of no consequence but what do you think?
After a 30 or 40minute drives,parked - on 3different days I got the following:
Cylinder Day 1 Day 2 Day 3
1 184 196 100
2 136 186 160
3 108 132 204
4 186 202 170
5 152 189 109
6 124 186 167

Relevant or telling in some way?

Thank you for listening
Darragh

I have the same engine as you (but in a C320), mine also had a lumpy idle I replaced the Maf with a non - original to clear another problem, which it didn't, so I used a genuine Maf which cured "both" problems, did you use a genuine Maf?
One more thing, white smoke normally means it's burning oil, you get black smoke from running rich.

 

[Darragh1]

Hi
Two fronts and tranny mount all genuine, done. they are not sided. They were checked and re checked. I so wish it was mount related, but it is not.
Exhaust mountings are good and properly placed.
MAF done , Bosch. Also a second Bosch tried out just in case and it is definitely not the MAF.
White smoke and a slight smell of petrol from the engine bay on starting in the morning. Maybe it s called lean but I thought a few mechanics said rich?

Props haft/central bearing mount...these may have been checked but would you mind explaining in a bit more detail what checks can be done? I know the flex discs are like new.

Chalpkin,sp!ke and grocer thanks and keep suggesting ideas.
Darragh.

 

[Terry_]

I know you are a long way but if you got the car to me I would be happy to get to the bottom of your problem for you.
There must be a sign in your values!!!!