ML320 codes PO300 Multi mis fire. - Mercedes Forum

sdanville · #1 11-27-2006, 07:06 PM

i have 120,000 miles on my 1999 ML320.

at 100,000 i replaced the CPS,spark plugs, fuel pump and filer as preventory maintenance.
last week it stumbled apon medium acceleration. when i drive like a granpa its ok pretty much.

reading the forums i thought it was the mass air low sensor. replaced that today with new. no change.

went to auto zone and got the codes. multi cyl misfire. he suggested plugs and wires. I dont think so. not all then cyl's with 20,000 miles on the bosch platinum 2 plugs.

I am thinking at this point cat converter. I have a recall and have been waiting months for the dealer to stock one for me.
i hear plugged cats cause this. my cat has rattled for about 2 months.
any suggestions apprreciated before i waste more time and money.

UPDATE: 12/7/2006 - Ran worse so went for a code reading again. this time all CYL misfires came up and fuel rail codes.
the Autozone guy said MAS. I told him i replaced it 200 miles ago. We decided to try fresh spark plugs. He had nothing good to say about any plug that has optional places to fire. (bosch platinum 2 to 4's.
I replaced my spark plugs that had only 20,000 miles on them. Went with cheap champion plugs as this was for diagnostic reasons.
Immediately after the truck ran okay. I had 5 minutes of bliss after the new plugs..then at a stop light it started the rough idle again..then the check engine light started blinking. So what ever my problem is, must have fouled the bosch spark plugs.

steve

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sdanville · #2 12-08-2006, 03:32 PM

today I had new cats installed and a vacuum line fixed. I dont know if it was one of those, or the computer reset or what..
But the Mercedes flew like the wind and idles so smooth I has to look at the tach to see if i was running.

12/17/2006 update. didnt take but a few miles after i wrote this and the rough idle came back and the check engine light came back on.PO170 PO173.
I ordered another MAS --- everything I read seems Imust have bought a defective New $100 Mass air flow sensor last month.I will update if this truck is ever cured.