rough idle when cold
Thread Starter
Newbie
Joined: Jun 2005
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rough idle when cold
Hey all,
I have a 2001 C240, and I've noticed when it's cold, my engine often idles rough, and/or will hesitate upon acceleration until the engine warms up. Tonight that got worse.. I went out and hopped in for a quick trip to the grocery store.. started the car and when I pulled out of my driveway, the engine suddenly hesitated really bad. I eased off the gas, let it regain it's idle, and then stepped on the gas again... it chugged for a min, then the check engine light came on.... I limped to the grocery, and when I came out, and started it again, it ran fine, but the check engine light is still on.
Any thoughts? I'd really appreciate help on this one.
I have a 2001 C240, and I've noticed when it's cold, my engine often idles rough, and/or will hesitate upon acceleration until the engine warms up. Tonight that got worse.. I went out and hopped in for a quick trip to the grocery store.. started the car and when I pulled out of my driveway, the engine suddenly hesitated really bad. I eased off the gas, let it regain it's idle, and then stepped on the gas again... it chugged for a min, then the check engine light came on.... I limped to the grocery, and when I came out, and started it again, it ran fine, but the check engine light is still on.
Any thoughts? I'd really appreciate help on this one.
Super Member
Joined: Dec 2001
Posts: 629
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From: PHILIPPINES
07' ML350
ive had that a long time ago...even worse
must be either or a combination of the following:
airmass sensor/MAF sensor
fuel injector
dirty gas tank (if u rarely use it)
spark plug (if u had bad gas)
as for me, i had all of the above b4.
must be either or a combination of the following:
airmass sensor/MAF sensor
fuel injector
dirty gas tank (if u rarely use it)
spark plug (if u had bad gas)
as for me, i had all of the above b4.
Thread Starter
Newbie
Joined: Jun 2005
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Well, I know it's not bad gas... It's my daily driver, and I have had this problem on any cold start for months.. last night was just the worst it's been by far.... I have no idea about the air sensor, or it could possibly be an injector or smething else... the car has 70,000 miles on it... most of which were prior to me buying it,s o I really don't know what maintenance was done and what wasn't...
I guess I'm calling the dealership today... lol
I guess I'm calling the dealership today... lol
MBWorld Fanatic!
Joined: Jun 2003
Posts: 9,498
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From: San Diego, CA & San Jose, Costa Rica & Stuttgart, Germany
1959 220S / 1979 230 G / 2002 A210 AMG / 2003 C320 SC / 2004.5 C320 SS / 2005 ML350 SE / 2008 smart
wow...
2001 C240
who would of thought ?????
2001 C240
who would of thought ?????
MBWorld Fanatic!
Joined: Nov 2001
Posts: 6,211
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From: Laguna Niguel, CA
With that amount of miles, just as a course of maintenance I would get the fuel injectors cleaned. Dirty or weak injectors can cause the engine to run too lean. I wouldn't say it's a sensor issue because most sensors like the o2 are bypassed during warm up as the ECU runs in open loop mode. During open loop mode the car runs on preset settings for timing and fuel. Since the fuel metering is fixed, dirty injectors can affect how much fuel the engine gets but when warmed up, the O2 sensors can detect a lean condition and compensate for it.
If cleaning the injectors doesn't do it, it's probably a weak injector. One thing I've been doing for many years is while cold, get an RPM reading, unplug each cylinder and jot down the drop in RPM. The cylinders with the least drop are suspect, of course no drop mean the injector is completely dead.
If cleaning the injectors doesn't do it, it's probably a weak injector. One thing I've been doing for many years is while cold, get an RPM reading, unplug each cylinder and jot down the drop in RPM. The cylinders with the least drop are suspect, of course no drop mean the injector is completely dead.
Thread Starter
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Thanks for the insight folks..
One more piece of info... I took it in to the MB dealer here, and they scanned the codes.. the only one that came up was one saying that a cylinder had misfired and was shut down... They cleared the code and told me if I have the problem again, to bring it in for service work..
does this change any of what you've said?
One more piece of info... I took it in to the MB dealer here, and they scanned the codes.. the only one that came up was one saying that a cylinder had misfired and was shut down... They cleared the code and told me if I have the problem again, to bring it in for service work..
does this change any of what you've said?
