sl600fanatic

I have a 1999 S320 W140 with only 11,000 miles on it, it is pristine except for this nagging P0170 code and a check engine light. I have not noticed any performance issues or noises but the check engine light is persistent and returns after less than 1 tank of gas (usually towards the end of the tank of gas). I have replaced the following:



1. MOT purge valve (check engine light came on curiously much sooner after this was replaced)

2. Manifold absolute pressure sensor part 011-542-06-17

3. gas filler cap



I also cleaned the Mass AIrflow sensor and the entire unit with MAF specific cleaner.

I did replace the MAF unit but got a check engine light immediately after so I used the original one again, and the check engine light went off for almost an entire tank of gas then came back.



Any other idea? Spark plugs are original from 1999 but only have 11K miles on them.

Frenchmann

Get a good OBDII scanner that can diagnose and run tests on your car's components. Otherwise you'll be on a wild goose chase trying to replace parts that might not be the culprit. A good scanner will run electrical signal to the components and be able to tell you which specific part is giving you the issues. Keep us updated and hope its an easy fix!
-IH

sl600fanatic

I have this code any ideas what it could be?

JohnLane

Air/Fuel mixture off.

Look for vacuum leaks/false air leaks. A smoke machine is your friend for doing this.

Fuel pressure can be off. The fuel pump, filter and pressure regulator are all old by now.

An oxygen sensor may be telling lies.

Injector(s) can deliver too much or too little. Read spark plugs for lean or rich conditions in individual cylinders.

sl600fanatic

Thanks I changed the MAF with a new Bosch unit and no more CEL