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Discussion Starter #1
Hi everyone. As the title says, my 2000 ml320 is not running as smooth as before. It runs fine and all but i can feel more vibration when i place my hand on the engine. Minimal hesitation while driving and minimal rough idle.

Been checking codes, check wires, plugs, o2 sensors (pre have been replaced and post are still oem). Everything checks out fine and normal. Air filter is new. Recently changed oil. Checked vacuum leaks, found one before but fixed it already. No leaks as of now. I havent check fuel filter though. Tappets are little louder that usual. Truck has 191,000kms on it.

Any thoughts? Theres no hardcore problem right now but just want to bring it back to what it used to be. Smooth and powerful.

Any suggestions are greatly appreciated. Thanks in advance!
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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I am unsure if "rough" means slightly rougher in the cabin, or slightly rougher in the engine rpm's.

If rougher in cabin vibtation, or getting thunky/jerky going from dirve-reverse-drive, then that mechanical issue can be rough mounts. Collapsed mounts can "feel" like misfires/rough idling.

If rougher in the idle-low performance, then: run a bottle of good injection cleaner thru the system (it takes a couple of tanks of fresh/good gas to feel full effect), do a ECU reset, consider a MAF cleaning, and pull one one plug (the electrodes thin out with mileage, you could buy one fresh plug to compare worn plug with fresh plug and decide for yourself if they need to be done) and if indicated by electrode wear reaplce all with OE equivalent Bosch.

That's what I would recommend to a friend.

MAF signs start with rough "gasping" when coming to a braked stop, where the engine RPM drops to idle and feels like it is choking.
 

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Discussion Starter #3
-Sorry for being a little vague.engine rpms i mean.
-very very subtle misfire if one can consider. Have done drive reverse drive test. Mounts hold up pretty well. I see no issues.
-cleaned maf sensor with sensor/intake cleaner.
-runs on 91octane minimum. Maybe i can try to use injector cleaner. A bit hesitant on which specific brqnd to use though.
-im not sure how to do an ecu reset and a bit uncomfortable to be honest.
-pulled out plugs, electrodes still prominent. Wires are golden.

MAF signs start with rough "gasping" when coming to a braked stop, where the engine RPM drops to idle and feels like it is choking.

-this one i have observed very quickly/momentarily just before the truck comes into a complete stop. So you think even ive cleaned the maf, its time to replace it? How can i test it? Any bench testing?

Thanks again for chiming in. Very informative and helpful.
 

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1999 Ml430
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191000 kms is 118681 miles... did you ever changed all the sparkplugs?
I run a full bottle of Techron Injector cleaner every 6 month through the tank, preferably on a long trip.
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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Your reply -

"MAF signs start with rough "gasping" when coming to a braked stop, where the engine RPM drops to idle and feels like it is choking.

-this one i have observed very quickly/momentarily just before the truck comes into a complete stop. So you think even ive cleaned the maf, its time to replace it? How can i test it? Any bench testing? "

You mentioned you previously replaced the MAF, and without knowing the source/maker of that replacement noone can vouch for the quality of the replacement - nor, do I have personal epxerience on the effect of the LP conversion (which could be nominal) on the MAF.

If any silicone spray has been used in the engine compartment, that kills the life of a MAF too.

On testing, you can do a forum search - the approaching idle on a braked stop "choking" hesitiation is a sign of contaminated or failing MAF. The running specs on the MAF are quite wide, and generally a CEL will trigger only after getting into extremely poor range. I replace before getting a CEL, and get myslef happy.

You have a challenge in the UK, since there are multitude more sources of not-exactly-OE MAF's in aftermarket there. Be cautious in your search for a replacement, make sure you are A-OK or you will get caught with another short timer MAF.

Keep the beat !
 

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Discussion Starter #6
I just cleaned the maf with maf sensor cleaner. I will be replacing the maf with bosch just want to make sure that it is the culprit. $150 value.
 

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I had similar symptoms which finally evolved into a failed start. Fortunately the CEL came on and the stored code pointed to a bad CPS. I am wondering if yours is in early failure.
 
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