E55 Rough Idle- Any thoughts
 

Two days ago I developed a slightly rough idle(tremble) , whether cold or warm. in park, drive etc when sitting still. There is a very slight stumble when initially stepping on the gas. Car has full power otherwise and runs like a beast. No check engine light or current codes for missfires. Stored codes for cat efficiency which I have had for about a yr and half off and on.... The car was tuned up a few months back with one step colder plugs, new wires and coils packs Reason being was random missfire codes in extremely cold temps. Check engine light would come on and i would also have a code p1999. Could the cats be causing the idle issue? Bad plugs all of a sudden? Thought about switching out for a replacement set of stock plugs. All vacuum hoses seem to be intact. I am scheduled for a dyno tune next weekend but now need to get this sorted out. Any thoughts?

:confused:

Maybe clogged fuel injectors. I had a issue where I didn't have a steady idle, turn out to be a bad crankcase ventilation valve. Honestly do not know!!

Happened to my M113 .. fixed by replacing Fuel Injector Valve O-Ring Seal Gasket A0199971348
Good luck!

I have no cats and car runs a bit rough when I first start it. Gonna take it to my trusty mechanic and see what he comes up with. Only codes are for o2 sensors on the cats.

Getting valve covers, wires, and plugs serviced next week, running some techron through it now as well, but I can't drive it much bc one of my tires is in bad bad shape (waiting on new ones to come in tuesday). So i'll let you know if that solves the problem

How many miles... I picked my E up with 120k on the clock and the passenger cat was so clogged it just blew in half after about a week of driving. The portion leading down from the exh runner "log" to the cat looked like an upside down funnel :-/ So I could see this as a possibility

Do you have anyway to see Afr to see if you could have fouled the plugs up by running dog rich during driving


Fuel, air, spark... shouldnt be that hard to triage I would think


Check to make sure all your bolts are firmly seated that hold the coil packs in that is how they are grounded

If you do not have a wideband just pull one of the front plugs and inspect if you can

Usually ,long tubes will make a little tuff at idle due to the amount of flow going threw the system.If the car is very shaky and can feel it even when the car is in drive ,check your coils,plugs and wires to make sure it's all ok.At 70k and up i would change all the 02 sensors to be on the safe side and there all reading correct afr mix.

Thanks guys. I know have 98k on the odo. I'm going to look into this tomorrow... Was trying to today but had too much to do. Was speaking with one of my techs. Was told there is no pcv valve being that it's
supercharged.. Definitely going to inspect cyl #8 as the missfire got worse early this afternoon while running errands and a fault came up with that particular cyl finally on my scan tool.. I know all wires are tight and intact because I checked before. Perhaps the coil went bad ( even though its fairly new) or the plug cracked? Not sure but will find out soon enough.. Once I cycled the key off and back on it went back to the slight tremble at idle but I don't want to do any damage to the engine so I must handle this tomorrow.

Update..pulled the plugs first from cyl 8. They were completely fouled out, totally black. I had NGK's one step colder installed in the beginning of March. Took out the remaining plugs.. They ranged from sooty black to brownish and they were all wet.. Went back to the stock NGK's LFR6AIX. Idle is a little smoother. I'd say 93% improved, but not 100%.. What gives?

I was going to say. I just did plugs today and night and day difference. I went 1 step colder as well.

Plugs should be this color

***Wet in my past was no good and indicated a blown or weeping head gasket. I have a hard time believing both banks blew and are spewing oil... maybe time for a compression test just to be on the safe side***

You are running too rich under load, what AFR do you see at WOT?

What are your IATs after blasting in 3rd and about 5k rpms in 4th?

IATs are prolly skyrocketing causing the ECU to pull timing and you are just dumping loads of fuel fouling it up... it will happen again unless you verify IATs/AFR and isolate the failure

while you are doing all this replace the fuel dampener. it can get clogged. possible the tune you put in is way off.

What other mods do you have OP? Just SC pulley?

supercharger pulley besides crank pulley, mhp 180 degree thermostat. no headers..just res delete

Maybe someone else can chime in but do you think you migh need better exhaust flow?

new plugs, wires, coils

98-2010 Mercedes Benz Spark Plug Ignition Wire Set Of 16PCS $102 shipped
1 step colder NGK (2309) LFR7AIX Spark Plug - Pack of 4 $26.65/4
Bosch 00107 Ignition Coil $55

Like I said ,at times they idle a tad ruff with headers more so long tubes ,but if your throwing codes, I would do as listed plugs coils wires

I got straight pipes up until the stock mufflers, so I'm guessing that's my issue on mine too.

Getting sparkplugs, covers, wires, and flexdiscs done at the shop tomorrow let's see how it turns out.

I actually had the wires ,plugs, coils, NGK one step colder spark plugs all done at the same time
with the valve covers and baffles back in the beginning of March.. Just removed the plugs sun and installed factory heat range since the colder ones were all fouled out