Rough/uneven idle, acceleration is fine

Tiny
FRANK BAUER
  • MEMBER
  • 2002 MERCEDES BENZ CLK320
  • 3.2L
  • 6 CYL
  • RWD
  • AUTOMATIC
  • 115,000 MILES
Hi. For about the past 10,000 miles I have noticed that my engine has had a rough idle (feels like it is missing at times) and the tachometer fluctuates. It was barely noticeable in the beginning, and sometimes it went away, but lately it has been worse and is now constant. When in drive it sort of feels like an engine that is lugging when pulling a heavy load. No Check Engine Light is present, and has recently passed New York emissions. I had the spark plugs changed recently (using OEM-specified plugs) since I figured the old ones were probably at the end of their expected life, but it made no improvement. I sprayed Seafoam into the air intake when doing the last two oil changes, which noticeably smoothed out the idle, but the effects was only temporary. Using fuel injector cleaners and DryGas in the gas tank has done nothing. Still accelerates smoothly and with plenty of power during both light and heavy acceleration, only the idle is the issue. It has not stalled on me (yet). I have also recently changed the air filter and checked the air intake hose, and nothing seems to be loose or disconnected.

Thank you in advance for any suggestions :-)
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Wednesday, May 11th, 2016 AT 12:27 AM

3 Replies

Tiny
KEN
  • ADMIN
Hey Frank,

We had this problem in the shop a while back and the problem ended up being the mass air flow sensor. What happens is the filament gets worn and doesn't deliver the correct feedback data to the main computer which leans out the fuel mixture.

Here is a video on what you are in for with the repair.

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and video

https://youtu.be/QOMiXhx2hbI

Let me know what you find

Best, Ken

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Tuesday, May 17th, 2016 AT 9:35 AM
Tiny
FRANK BAUER
  • MEMBER
Hi Ken,

I first tried cleaning my MAF sensor by spraying it with MAF sensor cleaning spray from the parts store (I disconnected it from the air cleaner, doused it and waited overnight for it to thoroughly dry, and then reinstalled it next morning). It ran fine for most of the day, and then my Check Engine light came on and the car started hesitating badly. The mechanic told me the MAF sensor somehow shorted out, so I now I had no choice but to buy a new one. However, I'm still having the rough idle. $340 in the hole, and the new MAF sensor didn't make any difference :-/
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Monday, May 23rd, 2016 AT 11:37 AM
Tiny
KEN
  • ADMIN
Hey Frank,

If it is only at idle the engine runs rough, it could be an injector is starting to plug or you have an intake valve that is starting to leak, and you do a compression test to see if any of the cylinders are low? Here is a guide to help you.

https://www.2carpros.com/articles/how-to-test-engine-compression

and

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let me know

Best, Ken

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Monday, May 23rd, 2016 AT 2:12 PM

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