The 740 has been a good car until a few weeks ago. I replaced the manifold to pipe gasket to quiet it down and everything seemed normal, ran better around the neighborhood and later headed for the store. I almost made it, but had sever power loss and it quit running. I pushed the 4000# beast myself to the store lot and called for a tow truck. Once I got it back home I tried starting it again and it ran fine for a few minutes then died again. I checked the codes and got 3 different ones, 221,231,121. Yesterday I removed the O2 sensor and soaked it in gas for several hours to clean it. After re-installing the O2 sensor the car started fine and ran for a good 15 minutes then quit again. It seems to run fine when cold but quits as soon as it gets warmed up.

My question is: What am I missing? It is an automatic, Bosch with 201,000 on the odometer

 

I've got the same exact problem with my 1993 240 wagon.

I had a vacuum code that was a bad hose.

Mine threw that 2-3-1 code as well, O2 sensor, I went and replaced it and no more codes but just like yours it will start fine and run for about 5-10 min. then sounds like it's starving for fuel/air and stall, but start right back up.

I'm looking at fuel pumps/relays now, will let you know what happens.

 

check your ECT temperature sender. check all the vacuum lines. if its got EGR, check that, as thats in the vicinity of the exhaust downpipe you were working on.

 

Mine ended up being the fuel pumps, but mine would only run for about 5 min. and then stall out.

That ECT is definitely worth a look. Once I could get to mine testing it was pretty easy (even for a novice like me). I was even able to follow the lines all the way back to the ECU/ICU, these guys are great!