dannyhrgl

Hey guys so when I purchased the car the car was shaking terribly at idle. I decided to replace all 16 spark plugs and wires with bosch oem parts. Additionally I changed the motor mounts and tranny mount with lemforder mounts. The engine mounts were collapsed and the fix helped. The idle vibration has gone down 70%, however, there is a slight vibration still happening. At times the car slightly moves side to side as well.

Could it be the coil packs as well? I am unsure on what the heck is going on?

tusabes

The 8 cylinder car use individual coils not coil packs like the v12, and problems with coil are rare in the v8

MB-Dude

Dirty or fouled injectors? Although MB purists cringe, I've had good experience with adding Techron or Seafoam injector cleaner to the fuel. No overnight miracles but results become noticeable fairly quickly. And I always run quality fuel, shying away from the cut-rate stuff.
Cheers,
Jeff

dannyhrgl

Yea i ran techron about 3 weeks ago so thats not it.

wallyp

Techron can be very effective, but it is not an instant cure. It can take a full tank of fuel, or even more, to clean a dirty injector.

The best way to use Techron or SeaFoam is with short-trip driving. This allows you to run the engine enough to get it warm, then let the fuel/Techron mix to sit in the injector as it cools. The repeated hot/cold cycles and extended soaking times over a week or two are much more effective than running a tank-full thru in a few hours on a long trip.

jnash

I would recheck carefully that you have solid connections on all your new wires to the packs and plugs, or that one or two are not mis wired.
Poor sea-foam in intake very slowly at idle and let the engine eventually flood and stop. Wait 15-20 mins, it will be hard to start and will throw a few emission codes. Reset those, and drive it hard. This will remove all the carbon build-up on the valves. Do this somewhere remote as it creates so much white smoke people will think there's a fire. lol
Use a can sea-foam in the gas tank for 3 fill-ups. then every oil change, poor seafoam in the gas tank. Ensure you have a new fuel filter before doing this.
There are plenty of youtube vids on poring seafoam in the intake.
Car should idle better, have more pull, and you should get better gas.
If this doent fix the rough idle, then do a compression test. If you have a cylinder down, typically cylinder 7 or 8, then poor some ATF fluid onto the piston and let it sit overnight to free the stuck rings.

tusabes

I think seafoam is more for neglected carboned up cars from the 1980s and 90s. Aren't most of these newer cars not yet at the point where they are likely to be carboned up?

jnash

My experience is that any car with more than 50k miles will show an improvement to seafoam in the air intake. Many dealerships have a de carbon system with full recovery of chemicals for this purpose and charge about $300. Seafoam is about $12 a can.