I have a 2012 Mercedes glk350 4matic. If my car idles over a few seconds it has a slight back fire to where the lights dim and the rpms drop to about 500 but if ur driving no noticeable difference. No check engine light. Has anybody experienced this before.

It could be as simple as a bad tank of gas, change brands and add a few cans of alcohol, Heat. get codes pulled. It could be many things. But bad gas happens often.

I think it’s the factory battery and I replaced the spark plugs at 66,000 so they have 6k on them

As a matter of fact I just poured in a quart of denatured alcohol in my Glk, it’s about 12$ a gallon a HD. It will be -4f in Chicago tomorrow. I’ve been doing this since 1968, I’ve never had a Gasoline related issue. Alcohol absorbes water so it can be burnt, it also raises octane, this is the simplest test, get a different brand of gas like Shell or BP and pour in 3-4 cans of the Red Heat, but the yellow can is good. With this deep freeze coming it’s good advise for all .

Definitely try a different gas station, and you are using premium. And add alcohol , otherwise it’s an expensive fix .

Only 93

93 is high octane , but gas is not gasoline . If I use Mobil , two blocks away, my glk and Volvo Knock. I go to BP or Costco and I get Zero knock. So my cheap **** Mobil guy is mixing the gas, cheating me, and not really selling High Octane !!!! Yes folks , it happens every day here with stations that don’t control delivery. That’s why ALCOHOL can determine many problems. It improves gasoline by removing water , and increasing octane . ( so a car can run)

I will never go to bp worst gas in st.louis I go to shell and the occasional sams club but I went to different shell and add some additives so far so good

Even If great gad fixes it , there is still an underlying issue