Conflicting Codes

[codabugg]

Seems my 91 LS400 is a little confused these days. I pulled the codes and got 25 (air-fuel ratio lean), 26 (air-fuel ratio rich), and 55. Last year, I was informed (by a Lexus dealer) that the 55 was a knock sensor and that it didn't really need to be replaced. Since then, the CEL has come and gone.

A few weeks ago, I pulled codes and got 25 and 55. I was told that the 25 was probably indicative of an O2 sensor, so I've been trying to find someone who can tell me which one(s). The other night, it started driving really rough (jerking) on the way home from work. When I got home, I checked the codes again and it had added 26 to the mix. It has been reset a couple of times and seems the 26 (along with the jerking) only happens when I drive this one route which has a fairly steep hill.

I took it in to the shop today to see if the scanner would give a bit more info to go on. The mechanic was stumped. He said he thinks it is either the MAF or the computer itself is going to hell.

Has anyone else experienced the conflicting codes (rich *and* lean)?? Any suggestions? BTW...what's the code for POS?

[SKperformance]

You may have a few problems not just one.

When was the plugs ,wires and a throttle body cleaning last done?

[codabugg]

You may have a few problems not just one.

When was the plugs ,wires and a throttle body cleaning last done?

All that was done last August.

[SKperformance]

Then i would get a motorvac to remove any additional dirt which may be clogging an injector and holding it open or closed.

[codabugg]

Then i would get a motorvac to remove any additional dirt which may be clogging an injector and holding it open or closed.

Thanks for the suggestion. I guess I'll just have to call around to find a shop who has that, right?

[LScott400]

If you are up for it, the 1st step on a Code 55 is to measure resistance between the KNK2 terminal of the ECM and body ground looking for 1 mega-ohm or higher. If it's lower, unfortunately, harness and sensor testing will be required and that means pulling the intake manifold.

If the reading is good, I would suggest opening the ECM and looking for leaking capacitors. Admittedly, my suggestion is biased by my recent Code 25 adventures. But multiple codes make me start suspecting the ECM.

I think the code for POS is 666. :)