Hi, I have a 96 S500 with a rough idle problem. Regardless of engine temp the vibration from idle is very annoying. Engine mounts are good and it drives fine. Any ideas what would cure this? Is it possible for the O2 sensors to cause this idle problem? Thanks

 

I would check the error codes. Usually helps in narrowing the possible causes and fixes. Any dash lights? 02 sensors are pricey. Try the error codes first.

 

no dash lights on and mercedes over here diagnosed knock sensors (which i changed). thanks for the info anyway. regards brian.

 

After changing the knock sensors, does it solve the problem ie rough idle.

 

changing the knock sensors didn't solve the problem. ordered up a code reader so i'll see if that tells me anything when i hook it up.

 

I had rough idle on my 1997 S420. It happened shortly after I changed the spark plugs. It felt like it was firing on only 6 or 7 cylinders. Took it to an Inde and diagnosed a coil pack problem. I probably nicked it up or something when I was changing the plugs, or it was just due for replacement.

They are about $90-$110 a piece, plus a little labor. I only had two replace, so not too bad. I might do it myself again if it happens.

Trick is knowing which cylinder is not firing, and that's where the error codes come in...

Let me know if you buy a code reader, I'd be interested in knowing what they cost and how effective they are.

Cheers.

 

almost all older S500 i see with missfires are because no one changes the cap and rotors. there are two on the front of the engine. under plastic covers. they should be changed or checked every 60k.