Well, I know just about everyone has had a problem like this in the past and there isn't *one* good answer, but since I am supposed to leave on Saturday morning for an anniversary trip 6hrs away, I figure that I need some help quick!

Since I have my 945's interior completely apart waiting for a heater core, my wife's '92 240 decided that it would be a good time to throw codes 231 and 221. This started during an 85mi trip about 20mi after getting gas. As soon as I could, I stopped to check and clear the codes. When I restarted though, the CEL came back before the idle even settled. FWIW, I think this is a lean condition (221 is according to the 7/9 faq but not according to the Bentley) since there is NO smell of fuel and no smoke.

I have checked high and low for vac leaks with little luck, the AMM was known good about a month ago (from another 240 that I sent to the 'yard), and the O2 sensor is about a year/40k mi old.

The only other thing that I can think of that could be related is that this car seemed to set ECT codes about once/six weeks. Every time though, I would reset and the code would not come back. It doesn't come on now either - only 231 and 221.

Any gems of wisdom?

Well, maybe my logic was flawed, but my diagnosis was correct. I replaced the ECU with one I had lying around and no more CEL. Of course, I replaced the bad white label 561 with a pink label 561. We'll see how long the replacement lasts...

I have also been thinking about the ECU. I will be pursuing that swap next.
thanks

All I can say is that I am dealing with the exact same problem.I have swapped both the AMM and the 0-2.I still pull a 221 and a 231 within 2seconds of starting the car,which seems to run fine.I am beginning to think maybe an intake gasket leak that only shows itself on start up? any help greatly appreciated.If I solve this I will post.Thanks

I would think that it would have to be a pretty big leak in the intake manifold gasket. Mine was changed at the same time as the O2.

Speaking of the O2, wouldn't it be *needed* along with the AMM to tell that the mixture was rich/lean? If I unplug it (the green wire) and start the car, I get the same codes right away. I was thinking that this might point toward the computer if the AMM is indeed good.