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Car idling and shaking

Old 02-11-2019, 10:42 AM
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clk 500
Car idling and shaking

Hello . I was washing my car this week and since we had snow i decided to clean up under the hood to get the snow and salt removed . We had a few nice days so i figured it will be the best time for this . I made sure the car was cold and i did not use any chemicals or high pressure hose . I used a regular garden hose without any attachment and kept the cleaning only inside the engine area . i even left the cover on the engine . After doing all this i dried up whatever i could and i let the car sit . when i went to turn it on it started normally but the idle was rough . If i am driving its not a problem it runs smooth but when i come to a stop it just shakes the entire car . I went and got a mass air cleaner yesterday and cleaned it and still doing the same . Wondering if you anyone here can point me to what can be the cause . I ran a scanner and i checked everything came back with no codes and no fault
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Old 02-11-2019, 12:03 PM
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2007 clk550 - Navigator - Frontier
You can get water into the wiring when cleaning under the hood. When I started having similar problems following the radiator catastrophic failure (dime size hole in radiator lower and pea size hole in top radiator hose), getting it replaced, cleaning residue after I got it back. My corrective actions were more extreme due to corrosion in a couple of wires from the coolant and overheating of the ECU. Through the trials of getting it back to norm I replaced the wiring harness, had ECU repaired, and replaced the spark coils (2 due to the issues).

In your case I would use compressed air to blow everything that may have gotten wet when cleaning. Also, I think it would be best to remove the engine cover first and cover the MAF with a microfiber towel. If you sprayed the ECU, you may also blow around the connectors and then reseat them.

BTW - I use MAF cleaner for cleaning the engine of oily grime and a plastic/rubber protector, applied to a towel, for cleaning other surfaces under the hood...

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Old 02-11-2019, 02:13 PM
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Make sure the engine cover is properly seated over the MAF sensor opening. Feel the backside of it with your fingers to make sure it's seated.
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Old 02-11-2019, 02:33 PM
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I drove the car already for about 8 hours in total over the past few days . I would think things will dry out by now . I took off the engine cover and i used lithium grease on the rubber boot on the hood cover and i made sure it seals . I unplugged all the coil power harness and made sure they are dry . I have an exhaust on my car so when i am at idle it crackles more than usual . Sounds like its running a bit rich . My gas millage is fine and no other issue but that and it shaking the car. I appreciate all the help
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Old 02-14-2019, 10:43 PM
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I've been having the exact same problem but I've never washed the engine bay.
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Old 02-16-2019, 03:14 PM
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2006 CLK350 Cabriolet (A209)
As mentioned already I would check from the spark plugs to the coil packs. My car had a similar problem in that it would intermittently start and shake...a year later and two trips to the dealership it has finally been fixed. Replacing coil pack number three cylinder did the trick. Took a year despite the fact that the computer was throwing number three cylinder misfire the whole time but “technician” chose to ignore that code. Finally took a picture of the code from my reader and had it noted when I dropped it off and told them to change it. When it did start and shake it was exactly as you describe, rough at idle but ok when up to any speed. This rough idle did cost me the replacement of an O2 sensor before it was fixed. Hope this helps.
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