you need to go to a muffler shop or another indie shop and have the pass side cat checked.if it failed the whole pass side bank is misfiring.
Start there.
next ,plugs are not a grand if you diy and a few simple tools and 12 plugs that cost $2.99 each for oem plugs and a sat morning under the hood and you can do it for less then 70 bucks tools and all.
codes p0300 mean multi cyl misfire p0301 mean cyl 1,p0302 cyl 2 ,p0303 cyl 3 they are all bank 1 which is pass side of engine,so something happened to trigger those codes and it was not 6 plugs at 2 per cylinder failing at the same time that did it.
have a good shop check the cat.then get it home and do you own plugs.
pm me if you need a diy link and i will look it up.
ohlord

 

Since the problem is one side specific it could also be the pass side engine injector harness wiring, O2 sensor or even the pass side air cleaner.
Did you have any rattling from the cat before this problem especially when cold?
Stuart

 

only one air cleaner on the e320,injector faulty possible but other codes would be shown likely.o2 sensor would cause the misfire condition but would also most likely throw a o2 code or a lt fuel term code like a bad maf.So I think he needs to start out at the cat and get it away from a shop that wants 1000 bucks for a two hour job and 12 spark plugs,they are raping him!!!!!!!!!!!
ohlord
diy plugs on benzworld.org w210 section or on mercedesshop.com diy section
17 mm spark plug wrench from me $25 bucks shipped included to u.s. destinations.
ohlord

 

Hi Ohlord.
My 320 M112 has two filters. One per bank. Maybe E Class is different for some reason. I wonder why if this is the case?
Agree that O2 would likely give an O2 code but not always.
Could be precat since this impacts O2 readings but the downstream cat has no feedback to the fuelling system other than if it is totally blocked. Possible but unlikely.
Think I suspect the engine harness insulation degradation.

I completely agree that it wasn't the plugs. they seem to run for ever.

Stuart

 

It happened to me on my 1991, 190E. It was the crankcase sensor.

Regards

Syed

 

Crankshaft position sensor.You meant,correct?
ohlord

 

A possibility BUT this would likely effect ALL cylinders, not just one bank.

CPS doesn't usually set a code when they start being temperature sensitive.

On thinking about this a little more I would like to know what the O2 levels are on each bank. A low cost way of eliminating the O2 sensors is to swap them over. does the misfire follow the change?

Stuart.

 

100,000 miles it is time to change all the o2 sensors anyway they are an 80 tho mile maint item.

 

any joy with the car problems yet, sounds more like the cat is blocked or sucked in,into the cylinders and its givin you major misfire.........hope not cause this leads you to a major strip down.......

 

Hi Ohlord,
The originator of this post PM'd me.
I asked for the complete service history and guess what!..... P0173, and P0170.
He wasn't sure the garage was correct so didn't want to have the MAF changed.

Stuart