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post #1 of 10 (permalink) Old 12-18-2008, 08:49 AM Thread Starter
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To the self-considered Benz Guru

Kay, Ill try and keep this short.
So on my way home from lethbridge to saskatoon, my Check Engine Light went on while i was driving at 120km/h. The car drove smooth, everything was in check, no high temps. So I stopped in the next town, and when the car is idle it's vibrating slightly. It would vibrate in D or P or R. So I turn it off, turn it back on and no vibration. I keep driving and under heavier acceleration the car will get this jerky, vibrate feeling, so I layed off that. It will only vibrate at a stop after Ive been driving for a decent distance already, and under heavy acceleration.
I took it to the benz dealership when I got back in saskatoon. They scanned it and it came up with 2 codes, P0300-080 (misfiring damages TWC),whatever that means, TWC? and it came up with P0304-083 (misfiring of cylinder 4 : 83.
The tech told me to start with the spark plugs, as they shouldnt go further than 4 years. Ive had the car for 1, so i dont know when they were last replaced. But why does the car stop vibrating in idle when i turn it off and restart it.
Also leaving the dealership the CEL was off, and as soon as I accelerated at a decent rate, it came back on, and I vibrated at the next red light.
Any opinions on all of this guys??? Other than spark plugs so I can cover all my bases.

What I don't understand is, how could this be a spark plug problem, if when I turn the car off and on the problem goes away until heavier acceleration? I would think this would have to be some sort of a reset thing like a MAF, as far as i know plugs dont "reset".

This forum gets alot more traffic then mine so i thought i might as well ask here too.
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post #2 of 10 (permalink) Old 12-18-2008, 09:07 AM
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If you have "shorter" version of the 320 engine so popular in US -the MAF would be the first suspect. IMHO with MAFs available below $100 that is still cheaper than reading codes at dealer.
Good luck.
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post #3 of 10 (permalink) Old 12-18-2008, 09:19 AM Thread Starter
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yah maybe ill order a new maf from autohauz, but the benz dealership here I am so impressed with, they didnt charge me a thing to hook up and pull the codes, and im not under any warranty at all. Good folks down there.
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post #4 of 10 (permalink) Old 12-18-2008, 09:42 AM
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My brother had a similar problem and error codes on the E-420 I bought from him. Ended up being a intermittent coil for one cylinder. Once a misfire is detected if it continues fuel is shut off to that cylinder until restart, supposidly to keep from damaging the cat. That is why it goes away on a restart for a while. One thing to try is to swap the coil with another cylinder and see if the code continues but with the new cylinder.


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post #5 of 10 (permalink) Old 12-18-2008, 09:45 AM
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Just went through this with our VW

A coil failed ie the electronic version of the distributor cap. In my case the I started noticing a small hesitation once in a while under heavy acceleration. Then poof about two days later the engine light came on and I had one cylinder that wasn't getting a spark so naturally the engine ran like crap. Low speeds you will get heavy vibration then as the non functional cylinder picks up speed the vibration goes away. The VW had one coil for each plug - they are like other electronic stuff some times they last years and years some times they just fail no reason etc. But when one coil fails VW mechanic said normally the others aren't to far behind.

Start simple and work your way up to the more complex. My guess is that the spark plug is probably OK but you could have a loose or bad wire if those things check out look into the coil as a possible culprit. Not sure if there is an easy way to test each part but my guess is there is an easy check I just have never done it.

Good luck
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post #6 of 10 (permalink) Old 12-18-2008, 10:36 AM
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P0300 is just a general random misfire. P0304 is misfire on cylinder 4. As suggested, change your plugs. I am not sure if you need to do anything with the MAF. Problems with that usually throw the codes P0170 and P0173. I would suggest you get some CRC MAF cleaner and clean it. I think changing the plugs will take care of the main issue. Good luck.

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post #7 of 10 (permalink) Old 12-18-2008, 11:55 AM Thread Starter
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alright will definitly do that, but another question, do i have to use the OEM bosch ones, because the benz here doesnt have any in stock and i dont want to wait for them to come in from vancouver so i was wondering if its okay to use an AEM spark plug?
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post #8 of 10 (permalink) Old 12-18-2008, 04:11 PM
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I vote for coil.

You may have a hairline crack in your coil. This happened to me. My indie showed me the coil and the crack was barely visible to the naked eye. Both my coils had to be changed.

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post #9 of 10 (permalink) Old 12-18-2008, 11:10 PM
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This could be something as simple as a bad batch of gas. I used to have an Audi that was very sensitive to bad gas which would cause a cylinder misfire code. Once in my Explorer I got a bad batch of gas which created hard starting problems. Did you gas up in Lethbridge at a place you don't normally use? An offbrand cheapo gas station by any chance?

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post #10 of 10 (permalink) Old 12-19-2008, 08:24 AM Thread Starter
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I filled up in lethbridge at the esso, 91 oct premium, then in swift current, i had a half tank left and filled back up at shell with the v-power. So it wasnt like a no name convenience gas store, but who knows maybe it is gas. Maybe Ill fill back up and see what happens, im at half tank again.
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