Question about 1999 Mercedes-Benz C-Class

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Mercedes c240 2001 low idle speed

Hi, I have a mercedes C240 2001 and just lately the idle speed has dropped to about 600rpm and the car feels like it wants to stall.
Any ideas ?

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Yes,check the fuel pressure & filter. There's about a million other things to cause this,so start simple. Ask again if this doesn't help.

Posted on Jun 21, 2009

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I bought a 2005 c240 not long ago. a week later it suddenly cut off when it dropped down into idle at a traffic light.Sometimes it sounded like an old V-8 duel exhaust sitting at a red light, or RPM's were all over the place, would shutter and cut off at slow speed or at stops, if it could idle it would idle high, had to sit with one foot on the brake and the other feathering the gas. Turning on the AC was enough to make it cut off (took me longer to find that out because I'm a windows down kind of person). I took it to a mechanic and they changed the MAF sensor and it ran well for a week or two. The back to same ole crud. I replaced the air filters and the fuel filter myself. Replaced the generic MAF the shop put on with a BOSCH, bought gas at different gas stations. Nothing changed. I was ready to drive it into the river and claim it as stolen, I was beyond over being the owner of a Mercedes. As last resort I must have tried every kind of fuel additive from the chain auto parts store. I figured it couldnt hurt, and made me feel like I was at least still trying. I ended up coming across a bottle of Mr. Gasket Cataclean. At $25 I wasn't sure if I was just letting myself be roped into another "miracle" fluid or if I should be sad that I've come to spending $25 dollars on a bottle of stuff that for all i know could just be big a big bottle of disappointment. Like when you open the bottle you actually hear the bottle say "sucker". You add this stuff when you have 4 gallons left, then drive around 15 miles, then fill back up. I had to drive a week before getting near 4 gallons but I finally got close enough and poured the bottle in. The next day... Runs like a dream (so far perfectly for 5 days - knock on wood) Idles silently at about 4-500 rpms - i keep checking to make sure its still on. No shake or shimmy. No problems at all. I'm completely shocked. Also completely mad that I was made a sucker out of by the mechanics and it was a plastic bottle of miracle fluid that actually fixed my car. Go try this stuff first - it is worth a shot.

Posted on Sep 30, 2014

  • Shannon Greer
    Shannon Greer Dec 22, 2017

    now that ive had the car a couple years.... here is what seems to have solved it for me. Other than the occasional miracle fluid to keep things clean on the inside the biggest thing i did that has removed all the rough idle issues was to remove the heads and replace the gaskets, replace the vacuum tubes, replace the throttle body and throttle body gasket, replace the coil packs.... And then of course keep up with very regular oil and spark plug changes. I believe the throttle body and coil pack replacements may have ended up being what really did the trick.


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Screw a high pressure fuel pressure gauge on the shrader valve on the fuel rail and see what your pressure is. If not 55-59 you have fuel pump problems. Also check fuel-pump relay inside of trunk, upper left on top. Make sure its not getting hot when this problem occurs. While you're there check fuel pump fuse(30amp) also on top/first one.

Posted on Jun 29, 2012

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