So I left work to drive back down to my apartment, on my way back I stopped at Costco to fill up, which is seemingly fine as they do carry top tier fuel. I drove 30 miles home and saw my radar hardwire kit was in so I decided to go back down and get it hooked up. I turned the car on and my RPMs were bouncing around a bit and the car started to shake, at this point I'm ****ing nervous since I've had the car (new to me) for 2 weeks. Drove around the block to see if it would settle back to normal- check engine light came on and still jerking. Parked, turned it off, and did that ECU/TCU reset and that seemed to solve the idle problem. Went for another spin and the car definitely responded to my reset, much smoother. Though the CEL was still on. Parked again and gave it some revs, noticed the car was much quieter, exhaust was less "slappy", and throttle was not nearly as sharp. Locked her up and went back into my apartment, CEL remains. Limp mode perhaps? I wouldn't rule out a tune by a previous owner.

I hope by tomorrow the computer might have figured it out but those are all the facts. Without asking me to buy hardware to check for codes can anyone suggest what may have happened? What I should look for, and what I need to do as to not blow up my new car? Need to diagnose this ASAP.

 

We need the check engine codes. Could be a bad O2 sensor or something. Any mods?

 

Without the codes it's hard. I will say I have heard issues with Costco gas. I personally will never fill my cars up with their gas even if it was a buck cheaper per gallon. Could very well be unrelated. Need codes. Autozone will pull what codes they can for free.

 

No mods that I'm aware of but I have yet to get under it to see if there was a res delete or something of that nature, haven't had enough experience with 63s to go off sound alone. I'll look into diagnostic tool.s

 

Thanks for the tip

 

Going off what you said, guessing what is wrong with your car would be pure luck. I hope you figure it out, but for us to help we at least need codes. These cars can become sensitive with air/fuel related issues which would be my guess which can also be a lot of things.

Could also be gas.

 

+1 autozone

 

I have a similar issue. Mine is a '12 and last week out of nowhere, the car started shaking violently and had a significant drop in power along with a CEL. It happened while engine was fairly cold still and under low load. I was just commuting to work leisurely. I pulled over and had it towed.

It turns out the cylinders on the left bank were misfiring pretty badly. An indy suggested maybe it is the cam adjuster solenoid that failed, but only based off the codes and description I gave. I took it to Mercedes for full diagnosis and they say the valve cover gasket on the left bank is the culprit.

The car is under extended warranty luckily and the dealership just got the go ahead to start disassembling the engine to "prove" to the warranty inspector that the gasket is indeed at fault. The car hasn't overheated ever since Ive owned it, but lately on cold mornings, the low coolant level warning pops up. But when you check, it is barely below the max line.

 

Damn let's hope it's not that, going to AutoZone on the way to work tomorrow. Fingers crossed

 

Dont understand how a valve cover gasket would do that. Maybe an intake manifold gasket?

 

On the M156, this remains to be seen.


But on my other car, boxer engine, I chased a vacuum leak for more than a month, it was causing a trim related code.


Turns out that the valve cover gasket, which is not completely visible in that car when you install it, folded during installation.
This caused the crankcase vapor recirculation system to breathe fresh air. The vapors in the crankcase are metered.
The fresh air going in through that system was not.

 

Update: Went to Autozone pulled code "P0301" Cylinder 1 Misfire Detected.

CEL is now off and car seems to be running fine though the throttle still isn't as sharp. Would the hard ECU reset remove a tune? Actually as I write this I'm still feeling minor misfires ¯\_(ツ)_/¯ I'm thinking I run it through a tank and see where I stand

 

Check coilpack for cracks

 

I started filling up at my local Sam's Club and noticed an immediate performance decrease. Filled up this morning at Shell and the difference is night and day. F Sam's/Costco crap gas.

 

Lots will argue with me (its almost as bad as an oil thread sometimes) but I am a firm believer in expensive gas = good gas. I refuse to fillup at anything other than Shell and Chevron.

 

Bad fuel, move one and forget.

 

Agree its bad gas. Exxon/Mobile or BP for me.

 

BP Premium is not top tier IIRC. Exxon, Mobil, Shell, 76 and Chevron are what I try to stick with. When I was on the east coast I used to also use Sunoco.

 

Like I said, shell & Chevron. Never used Mobil before. I think of all the gas companies, Shell is the best out of all of them.

 

Good news for you - hard ECU reset will not have any impact on a tune.

 

I'll argue with you!

Seriously, what you want to look for is Top Tier gas. It includes mandatory levels of detergents that will keep your engine from getting gunked up.

There are about 50 brands participating (see link below). In order to participate, ALL of the retailers grades and ALL of thier stations must qulaity.

Sams is NOT on the list, but Costco is.

http://www.toptiergas.com/licensedbrands/

 

BP premium is indeed on the Top Tier list. Confusion about BP premium may be a result of them listing regular and mid-grade as BP fuels, but they still call their premium 'Amoco Ultimate'.

All of the different refiners mix their gasoline in common pipelines and storage tanks. The only thing different about the tank truck load going to Shell and the one going to no-name-gas is the additives that get squirted in before the truck leaves the fuel terminal.
I'm aware of only one exception, and I don't know if it is still this way, but for many years Amoco Ultimate was the only fuel that was shipped and stored separately, ostensibly to maintain its superior quality.

 

Nah I understand what top tier fuel is. My confusion stemmed exactly from their separate listing of regular and midgeade fuel. Thanks for the clarification!

 

No argument, Top Tier gas is good gas.

Question is, is it necessary to keep your engine it's cleanest and provide the best performance? No, not really.

 

Then how come there is this thread and many others like it? Where people go out and fill up with bad / subpar gas and the car runs terribly?

I would say that is sacrificing performance.

And the basic knowledge behind higher octane gas is that it burns better/cleaner (for increased performance and to prevent knocking) which aids with keep an engine clean.

Can you get away with running subpar gas in your car? Yeah, I'll agree with you and say you can get away with it. But is it necessary to run it if you want maximum performance and longevity out of your car? Absolutely.