8 answers for rough idling and RPM drop at 50MPH

[tommyb]

Finally my car (97 528I) gave me all the anwers I needed for my thread dated 8/16/2004. the answer is CHECK ENGINE with the follwing 8 codes from table 11 based on My Peak Reasearch manual and code tables:

C8: Precat O2 sensor no activity cyl 1-3
CA: O2 sensor control limit, cyl 1-3
CB: O2 sensor control limit, cyl 4-6

E3: O2 sensor adaption limit, cyl 1-3
E4: O2 sensor adaption limit, cyl 4-6

EE: Misfire detected, cyl #1
EF: Misfire detected, cyl #2
F0: Misfire detected, cyl #3

Although I told you I have changed all 4 sensors, I have to assume the precat O2 sensors are defective since they've good connection and can be mixed since they are all one of the same.

The big question becomes: is all this misfiring in cyl #1, #2, and #3 related to the O2 sensors or is it a different beast. The car has brand new dealer spark plugs and no codes of 01, 02, or 03 related to problems in the ignition coils, thanks God.

Any thoughts top gunners out there????????? Thank you

 

[andreyiv]

What I can say is that from what I know the O2 sensors are only used to fine tune the mixture and the engine should run fine without them even being there, it will burn more fuel and eventually this is known to ruin your cat/cats but it should run without misfiring on any cylinders. This said the sad part is that if it all that is true, you got a problem somewhere else. Something tells me though that it is O2 related because with newer cars they rely more on electronics than on mechanics. Try and see if the codes come up again.

 

[tommyb]

Andreyiv

yes you are right I used to get 27MPG prior to the problem with the O2 sensors. Now I am still getting 20.1 to the Gallon and starting to smell unburned gas on cold start. Today's codes (all the Cs and Es codes listed above) l are telling me the precat O2 sensors are defective (gas mixture) not the AfterCat ones (emmission stuff)

But still the puzzling part is this misfiring. I am still not sure if they are related. I guess we'll wait and see other answers. Meanwhile I'll change both precats again (one month old and now no sensors activity) at least to eliminate that possibility. Thanks