98S420(W140) CEL on CODE P0170

[smk_texas]

Hi Folks,
The CEL came on this morning in my 98 S420 (72K miles). The following were some of the symptoms that preceded the CEL.

1. During the last month or so, on a few occassions whenever I stopped at a light or stop sign the engine would shake a little and felt like it was going to die but never did. It would idle just above 500 rpm and after a few seconds went up to normal idle.

2. Whenever I accelerated from a stop sign/light the accelerator pedal felt hard and there would be no engine response for a few seconds. However after I depress the pedal halfway the car would take off normally.

Finally today the CEL came on. I used my AutoXray OBDII scanner to read the codes. It showed P0170 - Fuel Trim Malfunction < Bank 1>.

Any help/suggestions would be appreciated. Thanks

smk_texas
98 s420 72k
03 ML500 71k

[arkie]

P0170 is not a "direct" code - it is an adaptation code. In other words, the engine is trying to compensate for something and it is no longer within tolerance. Your symptoms sound like a Mass Air Flow sensor acting up - but your are guessing at things without taking it to someone with a system that will look beyond the OBDII codes and look at actual values and adaptations. Take it to a good shop, otherwise you will only solve your problem by methodical parts-swapping and that gets expensive.