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1998 ML320
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19 Posts
Discussion Starter #1
Hey guys,
For about a month or two now, my mileage has gone down from ~15-16 MPG average to 11-12 MPG. I do mostly city driving, my commutes are about 4 miles each way so the engine is warm for only about a quarter of the commute. Also, it's been about 10-30 degF outside.

Could my horrible mileage be from just the cold weather???

Also, I noticed while I was driving on the highway that at times the engine will seem to "waver". I wont change the position of the gas pedal and the tachometer needle will seem to move back and forth a few hundred RPM (like 2000-2300 RPM).
 

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05 500
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6,516 Posts
Even 15-16 for the 320 seems low. I used to have a 02 320 and the mileage was not that low. In any case, we know you have a problem but I can't help you because I don't know what the solution is. My experience has been that air filter replacement and tranny service on these truck boost mileage considerably. Hope that helps a bit!:mad:
 

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Registered
1998 ML320
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19 Posts
Discussion Starter #5 (Edited)
Even 15-16 for the 320 seems low. I used to have a 02 320 and the mileage was not that low. In any case, we know you have a problem but I can't help you because I don't know what the solution is. My experience has been that air filter replacement and tranny service on these truck boost mileage considerably. Hope that helps a bit!:mad:
im thinking i might replace the air filter. the tranny is questionable, i've made a post about it before, but i suspect theres something wrong with it.

if i am traveling +50 mph, then gradually slow down to around 18 mph while keeping my foot on the gas, and just touch the gas pedal a little bit more, i get this pretty strong vibration coming from the engine, and it sounds like its struggling. this happens at ~18mph, and also around ~22 mph :surrender:

Edit: I just checked the air filter, it was replaced only a few months ago and it's still clean, no obstructions
 

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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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7,035 Posts
How about when you come to a braked stop ? Other

When you are coming to a braked stop - sometimes the the engine RPM seem to choke/dip almost below idle, then recover ?

Have you need hearing any "metallic rattling" sounds from underneath the car at idle or when driving as the engine warms up ?

When were the spark plugs last replaced, and if so replaced with what plugs ?
 

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ML320,C230, F250, Bayliner, Mountain Bike, Fleetwood Motorhome etc...
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1,836 Posts
You may have plugged catalytic converters. I had the same problem. The front one comes apart and plugs the back one with debris.
 

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Registered
1998 ML320
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19 Posts
Discussion Starter #8
When you are coming to a braked stop - sometimes the the engine RPM seem to choke/dip almost below idle, then recover ?

Have you need hearing any "metallic rattling" sounds from underneath the car at idle or when driving as the engine warms up ?

When were the spark plugs last replaced, and if so replaced with what plugs ?
I'll keep an eye out for the choke when slowing down, though I haven't noticed it. Is this something I'd only notice by watching the tachometer or is it audible?

I have not heard any rattling when idle or cold.

The spark plugs were replaced less than a year ago by the dealership, so I assume they're OEM (Bosch?)

You may have plugged catalytic converters. I had the same problem. The front one comes apart and plugs the back one with debris.
Is there a way for me to check the cats or do I have to bring it in?
 

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2000 ML430, 2000 C280
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920 Posts
I had a similar problem where my gas mileage was below par even though my spark plugs were recently changed. In my case it turned out to be a bad ignition coil and wires, but not bad enough to throw codes when driving normally. I did get a cylinder misfire code one time at very high rpms, but that was during very atypical driving (near redline) so you may not notice this. Have your ignition coils and wires checked before going on to more expensive options.

DelJ




...The spark plugs were replaced less than a year ago by the dealership, so I assume they're OEM (Bosch?)...
 
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