zz4x4

I have a 2000 S430 that has always idled very smoothly. Recently I began to have random misfire codes. I replaced all 16 plugs with NGK platinum. The old plugs' electrodes were definitely worn away. Good news is that the misfire codes are completely gone even after 2000 miles. Problem is that I am now experiencing a very rough idle. RPMs are steady and power is good. My question is ... could a bad plug cause a rough idle yet NOT set a misfire code? I have replaced the plug wires since with no effect on the rough idle. I am leaning towards engine mounts at this point, but still a funny coincidence that they went bad right after a spark plug change.
Any thoughts?
Jeff

my06clk

If you haven't changed your mounts before then that is more than likely the issue.. there is no such thing as a smooth idling s class with collapsed motor mounts..The fact that your rpms are good is a good indicator of the problem

benz_addict

I have the same problem ho wmuch am I looking at $$$ to get them replaced at the stealership?

Also what if they don't get replaced would it have any negative impacts on anything?

my06clk

The mounts are $118.00 dollars for the set. and are a simple but time consuming DIY. Dealers will charge at least 7 hrs labor so do the math.

When these mounts collapse, the olnly this you will get is the vibrations at fist. If you et then go, the rubber will break and you will have nothing supporting your engine to the frame so it will start moving when you accelerate causing loss of torque and possible damaging the tranmission mount if it isn't already..

This is not something you want to let go forever...I will do mine in a few weeks and post pics of the process so you will be able to see if this is something you want to do yourself.

benz_addict

you really are a valuable member on this forum if you make a DIY I will make some paypal donations

my06clk

Thanks..

And you're on..I'll post my paypal address when I finish the DIY .. I should get to it next week when I return home...

benz_addict

do you think only the tranny mounts need replacing or all of them? My car vibrates badly from 100-130km/h you think this is related with the mounts? Does this with my stock wheels and the 19s

my06clk

It Depends , I'm thinking just the two motor mounts but I wonlt know for sire till I get into it.

As far as the vibration question,

NOPE. No at all..

THat is another problem..YOU need to re-evaluate your wheel situation.. Just because it does it on both sets does not means hat there isn't issue with both sets..

Speed dependent vibration 99% of the time is wheel/Tire related.

02S430

any update?

zz4x4

For the archives...I replaced the engine mounts and it solved the problem. The idle is completely smooth now.