Codes PO300 '99 ml320 cat ?
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
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From: Western Michigan
ml320
Codes PO300 '99 ml320 cat ?
120,500 miles on the 1999 ML320.
At 100,000 I replaced the
Spalrk Plugs
Crank Shaft position Sensor
Fuel Filter and Pump
at 120,000 miles it started misfiring on medium acceleration.
then idle rough. I could restart at stop lights and the idle would smooth.
Reading the forums I thought Mass Air Flow sensor. cleaned it a couple times then bought a new one. No change.
Seems better in warmer temps. If I drive really really easy its usable but not too safe if I need to scoot.
Auto Zone guy said codes PO300 multi cyl misfires then reads off every single cyl. PO301 to PO306. He said wires or plugs. I dont buy that. all at once ?
I am waiting for my back ordered Cat converter thinking restriction. Im all ears if anyone has fixed this. steve.
At 100,000 I replaced the
Spalrk Plugs
Crank Shaft position Sensor
Fuel Filter and Pump
at 120,000 miles it started misfiring on medium acceleration.
then idle rough. I could restart at stop lights and the idle would smooth.
Reading the forums I thought Mass Air Flow sensor. cleaned it a couple times then bought a new one. No change.
Seems better in warmer temps. If I drive really really easy its usable but not too safe if I need to scoot.
Auto Zone guy said codes PO300 multi cyl misfires then reads off every single cyl. PO301 to PO306. He said wires or plugs. I dont buy that. all at once ?
I am waiting for my back ordered Cat converter thinking restriction. Im all ears if anyone has fixed this. steve.
Newbie
Joined: Nov 2006
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Ive seen once or twice, cats so clogged up it causes a missfire. From what it sounds like its a MAF, but i wouldnt replace it till the cats are replaces. The plugwires could be bad too, but when those go the motor seems only to have a skip not a complete missfire. Id wait to see if the cats fixes it.
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
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From: Western Michigan
ml320
Misfires continued
Thanks for the reply. The more I read the more it seems a plugged cat would effect the plugged side not mis fires on all cyl.
1) I replaced the Mass Flow Air Sensor. Bought a new one off ebay for $100.
No change. But then I disconnected the battery for a night and it seemed better.
2) Then I jump started a 90 year old man in the bank parkiing lot which I read we shouldnt do. (jump start cars with Mercedes).
3) I reset the transmission brain ( per forum instructions ).
I noticed it starts with a bit of a rev like it use to again,,
My ML320 doesnt feel perfect, but I am getting along. The streets are snow and ice here so I have not done anything close to agressive accleration.
The reason I reset my transmission, I made a stop on a street..put it in reverse to back into a driveway...nothing happened..then I put it in drive and nothing happened...after a few seconds with traffic coming down on me fast it engaged in drive.
I really want to be an optimist..but I am really ready to ban Mercedes from my contenders in my next purchase. Just bought my wife an Equinox. not even close to the enjoyment of driving the ML320. But I trust it. So It will be driven to Florida this month.
1) I replaced the Mass Flow Air Sensor. Bought a new one off ebay for $100.
No change. But then I disconnected the battery for a night and it seemed better.
2) Then I jump started a 90 year old man in the bank parkiing lot which I read we shouldnt do. (jump start cars with Mercedes).
3) I reset the transmission brain ( per forum instructions ).
I noticed it starts with a bit of a rev like it use to again,,
My ML320 doesnt feel perfect, but I am getting along. The streets are snow and ice here so I have not done anything close to agressive accleration.
The reason I reset my transmission, I made a stop on a street..put it in reverse to back into a driveway...nothing happened..then I put it in drive and nothing happened...after a few seconds with traffic coming down on me fast it engaged in drive.
I really want to be an optimist..but I am really ready to ban Mercedes from my contenders in my next purchase. Just bought my wife an Equinox. not even close to the enjoyment of driving the ML320. But I trust it. So It will be driven to Florida this month.
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
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From: Western Michigan
ml320
UPDATE: Dealer installed catalitic converters. When i brought it in he asked "anything else?" i said it misses but want to see what the cats do before i commit. 4 hours later he comes in the waiting room and says they found a vacuum line malfunction. $80. labor. I was just happy to be done and have it idling good. I will never know if it was the cats, the computer reset, or a vacuum line.
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
Likes: 0
From: Western Michigan
ml320
I spoke too soon on the smooth idle. Ordered ANOTHER mass air flow sensor. I checked my resistance on one bank of ignition wires. all in the same range but dont know where they should be exactly. maybe one faulty thing snowballed into 3 or 4. the spark plug replacement helped. The MAS helped. The new cats helped. but once in the last ten drives i went to pull ou in traffic and took a minute to get up to 60 MPH. Embarasing and dangerous. Thats when I ordered another MAS.
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
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From: Western Michigan
ml320
vacuum line location.
The service tech was vague- real vague.
He said...
"The mechanic insulted whomever was working on this because in the back of the engine there was a vacuum line kinked or routed wrong and he either replaced it or corrected. It was in the back of the engine hard to see ".
I have taken the plastic engine cover off and looked with a flashlight and mirror over and over hoping to find a split vacuum line or one disconnected.
I drove it 150 miles in the last 24 hours. ITs fine warmed up on the XWay but at stop lights it misses terrible. I am taking my reliable Chevy to Florida tomorrow. In two weeks I will be at it again...trying to cure the Mercedes.
He said...
"The mechanic insulted whomever was working on this because in the back of the engine there was a vacuum line kinked or routed wrong and he either replaced it or corrected. It was in the back of the engine hard to see ".
I have taken the plastic engine cover off and looked with a flashlight and mirror over and over hoping to find a split vacuum line or one disconnected.
I drove it 150 miles in the last 24 hours. ITs fine warmed up on the XWay but at stop lights it misses terrible. I am taking my reliable Chevy to Florida tomorrow. In two weeks I will be at it again...trying to cure the Mercedes.
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Newbie
Joined: Nov 2006
Posts: 12
Likes: 1
need info
UPDATE: Dealer installed catalitic converters. When i brought it in he asked "anything else?" i said it misses but want to see what the cats do before i commit. 4 hours later he comes in the waiting room and says they found a vacuum line malfunction. $80. labor. I was just happy to be done and have it idling good. I will never know if it was the cats, the computer reset, or a vacuum line.
Thread Starter
Junior Member
Joined: May 2004
Posts: 36
Likes: 0
From: Western Michigan
ml320
Free Zip -0- Nada
The Cats Cost me -0- NADA , zip, Nothing.
Recall for my 1999 ML320.
I have both done for FREE.
I said to the service guy when leaving...guess I saved a couple grand eh ? He said more like $3,000.
Recall for my 1999 ML320.
I have both done for FREE.
I said to the service guy when leaving...guess I saved a couple grand eh ? He said more like $3,000.
