AMG3.2

Hi all,

This has happened a couple of times now. I go start the car, and the car just idles a bit rough. Nothing too extreme, but enough for the girlfriend to ask "what's going on?"

No codes, no CEL, nothing. Car drives and pulls well all the time and starts up well 98% of the time!

Any ideas on what to look for?

Thank you!

SROC276

Most likely winter blend gas....I switched to chevron and doesn't happen as much. Had this issue last winter using shell or 76. If it starts to idle weird, shut off then restart. Should fire up better. hard to pin point for me. Thought it was vapors, fuel injector, rail, tune ,o2 sensor...but nothing...just changed gas after a few weeks of troubleshooting. Change of gas worked almost immediately for me. High methanol mixed winter blend for California has been an issue for some.

m a x i m u s

Just a question, what's the deal with winter blend and summer blend? Why don't we just have "gas"? Seems like the blends are the cause of issues with our cars.

SROC276

I believe it's mostly for enviornmental emissions issues that states switch between blends. exhaust gases from vehicle react differently in warm and cold climates...additives are added in winter blend that allow for a higher cleaner burn rate than summer blend. Plus I think this m156 or any Benz 8 cylinder has been sensitive to it for some reason. Benz has no fixes or are only temporary. I just changed gas and so far, no issues this winter. Chevron has least amount of ethanol in their blend so something to do with that I think.

m a x i m u s

Interesting. Thanks for the reply.

AMG3.2

Hmmm strange. Car started up perfectly fine today so not much to say I guess. Thanks for the input on winter gas, though.

SROC276

Yup, the issue is intermittent and acts up randomly. Just saw your picture in the thread and you were filling up the tank...might be a good clue...lol

CarHopper

winter vs summer gas

http://www.popularmechanics.com/cars...ence-13747431/

jcdenton

Sorry for bringing up an old thread, but for archival sake, Shell gas seemed to cause issues for me also. I was using Shell 91 (the highest they had near me at the time), and occasionally I would get a "running lean" CEL code. Not too long after that my fuel pump failed, apparently due to clogging.
Later, they introduced Shell 93 near me, and that seems to be better, but I would still get occasional rough idles briefly on start, but would otherwise drive great. Then I switched to Chevron 94, and it seems to run nicer, and also get slightly better fuel mileage. For the record I'm in Vancouver, BC

SROC276

Chevron 94? Nice all we have here in CA is Chevron 91 because we are “special”.

After some time messing with the gas to resolve idle and code issue, there may a few things to consider other than gas. My issues were resolved when I replaced my PCV which tends to go out or start to around 40-50k miles from what I’ve gathered. Some resolved their issues by either reseating their intake box, checking if any air leaks before MAF, cleaning their MAFs, replacing intake manifold gasket due to leaks, replacing PCV (main one for me) and some other one off fixes.

Helped too to do a BG44 cleaner for the fuel system. All depends on how many miles and how you drive but it’s a great cleaner.

thanks for input and great on the Chev 94….it’s what dreams are made off here in CA