I own a 98 slk 230, lately it has hesitated when trying to increase speed. it seems like it is going to back fire. I thought it might be the humid weather. I changed a mass air flow meter around 6months ago. I put some fuel injector cleaner in it. and just ordered new spark plugs. the ones in it are only a year old. so I am not sure what it is that is causing the power loss when flooring the gas. could it be a fuel filter or computer problem?

When you changed the air mass sensor(6 months ago) WAS it coated with oil?? Have you inspected that air mass sensor for oil now?

The early Kompressor engines have problems with PCV system that can cause a back-up of oil into the air intake & then into the air mass sensor. Replacement of PCV valve & modified valve cover hose can rectify that problem.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

yes it was coated with oil. I havn't chked this one yet. I had a different air filter before and I changed it back to the factory.

does this mean i have to buy another air mass flow. that was expensive, I wish they would of told me that before. how hard is it to put in a pcv valve and how do I modify the valve cover

Most likely the air mass sensor is "toast", however try cleaning with AIR intake cleaner.

The modified HOSE part number for the valve cover is 111-018-16-82 & the PCV valve number is 111-010-00-91.

Also the connector on that hose must have at least a 2.5mm hole to allow vapors thru at full throttle!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

thanks for your help, they didn't have the pcv valve they called it a check valve... is that the same thing?

MB parts guys don't have a clue about PCV valves as MB hasnt used them for 20 + years! That number is for a PCV valve! A PCV valve is a check valve!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

thank you I ordered both, I will look at them, I hope they are easy to put in. I also noticed a rubber hose in my air filter lid that was all bent out of shape, I just took it out. will that effect anything without that rubber attachement? it looks like the air goes to the same place, it just went through rubber instead of free air.

Be careful to drive the car until you have cleared the problem.

I just had exactly the same symptoms (w140 300SEL) with lack of power, and I contiued to drive (carefully though) while searching for the problem.

The problem was indeed the air mass sensor causing too lean mixture. With lean mixture the catalytic converter gets hot and eventually burns down. And when it burns down the internal breaks into peaces and fills up the muffler system with the destroyed catalytic converter.

Total repair cost $4.000.

The air mass sensor is only $500. Expensive, yes, but cheaper than the consequences. Not to talk about if also valves were burned.

Good luck with your repair.

__________________
1991 300SEL (W140)
1987 190E 2.3 (W201)
1987 Honda Accord 2.0

I'm wondering if this is indeed the issue on my C230. No codes exist, at least that could be scanned by Autozone's free service (and I have no CEL).

Same symptoms, AND I have noticed a burning, rubbery smell when leaving the car for the past month. Burning cat? Crap.

I have no reason to think the MAS has been replaced in the car's 104k life. Then again, I did run a nice dose of techron maybe 2 weeks before this started happening, but I have run techron a half dozen times before.

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

Were you using a K&N filter by any chance...?

__________________
'01 SLK320, '79 450SL & '01 C320 -- What? 3 Mercedes? I am DEFINITELY crazy!!!