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2001 SLK 230
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493 Posts
Discussion Starter #1
My 2001 SLK230 (automatic transmission model, 48K miles) has had its idle change over the past week. The car used to be totally smooth when in Drive, as in you couldn't tell it was running smooth, and it idled about 600 rpm. Now it has a little vibration when it is in Drive, and idles about 700 rpm. Just enough to feel it in the steering wheel. No misfirings, just rough. The check engine light has not come on. The car runs like it always has at all speeds.

6000 miles ago I replaced the plugs and installed a K&N filter.

From previous posts, I am wondering if it might be a mass air flow meter problem? Someone had mentioned that a new MAF made their car idle smoother and at a lower rpm. Should I try to clean the MAF?

I am wondering if the MAF might have some oil contamination. K&N filter or crankcase breather problem?

The breather hose in the following pictures seems to get a little wet with oil at the valve cover. It was thoroughly cleaned a couple of thousand miles ago, and now you can see some oil seepage and the hose is slightly wet with oil.

I've seen recent postings about air injector bypass valves causing the MAF to go bad, but I'm not sure that my car has the same injector bypass valve. The posts I've seen have been for pre-2001 models. Is there still a bypass valve that I should check on my newer model?

I know there's a lot of questions here. Thanks for reading this post.
 

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Registered
2001 SLK 230
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493 Posts
Discussion Starter #2
I cleaned the MAF. It didn't change the idle. Everything looked very clean in the intake, as it should.

Maybe it's something I'll just have to watch for a while to see if it gets worse?
 

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'98 SLK230, 2007 Black E63 AMG
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189 Posts
It will get worse... my slk had a bit of a rough idle when I got it (about 7 months ago) and now it is considerably worse. I can actually feel the car shake a bit every once and a while when idling...

I though I would just ask my dealer about it when its due for the next service.

PT
 

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2001 SLK 230
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493 Posts
Discussion Starter #4
I put in a new set of Denso Iridium plugs, cleaned the MAF again, and unhooked the battery for an hour. No real change, still rough in gear.

While looking for a vacuum leak I may have found part of the problem: The plastic engine trim plate above the intake manifold had cut partly through the 1 inch hose connected to the injected air check valve. I could see some cords in the hose, but I'm not sure that it was cut all the way through. I wrapped tape around it, put it back together and fired it up. The vibrations are much less now. Not totally gone, but significantly reduced. Maybe a day or two of driving will let the computer smooth out the idle.
 

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2001 SLK 230
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493 Posts
Discussion Starter #5
Problem fixed!!!

Answer: Too much transmission fluid in the AT.

How much? About 200 cc too much.

I couldn't believe it. I changed 3 liters of AT fluid a week ago, and had just slightly overfilled it. As in the fluid was 1/8 inch above the top mark after driving 30 miles on an 85F day here in Houston. Well, that was too much.

I decided to take some fluid out, and as soon as I pulled out about 150-200 cc, the idle picked up about 100 rpm or so, then settled back down. I put the car in drive, and it was smooth. I went ahead and took a little more fluid out until it was at the minimum "full @ 80C" mark.

How's that for a weird story?
 
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