My check engine light comes on an hour or so after resettting the computer. I get code P0170- fuel trim malfunction. I have cleaned the MAF sensor, new oxygen sensors, new plugs and air filter, and cleaned the throttle body. Any ideas on this??? Thanks, fred fisher

That does not work. You'll have to hook the car up to SDS and read the adaptation values to get a better diagnosis.

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John Shellenberg
1998 C230 "Black Betty" 240K

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never read of anyone cleaning a MAA/MAF successfully - has to be replaced

Before getting too deep into engine management, see if there is any fuel coming out of the vac hose at the fuel pressure regulator and check for vac. leaks..
both will bring up a trim limit code.

You Wrote"My check engine light comes on an hour or so after resettting the computer. I get code P0170- fuel trim malfunction. I have cleaned the MAF sensor, new oxygen sensors, new plugs and air filter, and cleaned the throttle body. Any ideas on this??? Thanks, fred fisher"

Fuel trim errors are mostly caused by the O2 sensors reading a lean condition. Lean, meaning "not enough fuel". If the Fuel Filter is plugged up you will "not get enough fuel". If your Fuel Injectors have excessive varnish built up on them you will "not get enough fuel", If your Fuel Pressure is not correct, you will "not get enough fuel". Do you see where this is going ?

In your list of items replaced, I don't see Fuel Filter.

If it was my car, I'd check the Fuel Pressure to rule out pump or regulator, analyze the fuel trim adaptation numbers, then based upon the findings, I'd procede from there.

If I didn't have the pressure gauge for the fuel system pressure test, I would replace the fuel filter and run some high quality fuel injector cleaner like Red Line through a tank full of "good" gas. Reset the light and see how you go.

Let us know what you end up doing.

Fuel trim codes aren't caused by O2 sensor problems! FUEL trim means that the ECU has gone to a max lean OR rich adjustment. ON MB's that is almost always caused by fuel pressure OR incorrect info from air mass sensor or a vacuum leak!

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What I should have said is, "that in my experience", it has always been due to a lean condition.

The message I was trying to get accross is..... do the obvious stuff first.

ie... If the car hasn't been tuned up in a while and it runs like crap, a good place to start would be to tune it up.

A fuel filter is a small price to pay for something that "could" realistically fix this problem.

Please remember, I'm only trying to help.