Check Engine Code 1221

[fastair]

I have owned my 1990 325i for the last two years. During that time done all recommended maintenance, timing belt, tensioner, thermostat, water pump, water and vacuum hoses, plugs, ignition wires, distributor cap, rotor, blue water temp sender, radiator, starter, rebuilt the fuel injectors, valve adjustment, as well as a new BOSCH O2 sensor. The car was running great with no problems. Yesterday the car was extremely difficult to start, never done that before. It finally started and I shut it down and tried again, same thing, very difficult to start. I did a stomp test and got the 1221 code which is for the O2 sensor. The car was still running good, except for the starting issue. I took the connector where the sensor plugs into and wiggled the wiring. The car immediately started as it always had. Thought the problem may be some corrosion on the plug. Today I cleaned the contacts with electrical contact cleaner, reassembled everything with dielectric grease. The car started immediately and ran great. On the way back to the house the check engine light came on and is staying on. Yesterday it only flashed and then went out. The car seems to be running great, idles good, only now I have the check light on. The O2 sensor is not yet a year old, suggestions.

[cheffy30]

damn. might have to think about parting it out... sent from hell using Tapatalk

[Northern]

My 1990 325is did this same kind of crap when it still had the M20. Never figured out what was wrong, but would randomly idle like crap, throw a CEL for 1221 (Lambda Control) and then be fine after a bit of throttle.
C191 seemed clean on both sides. I replaced plugs, cap, rotor, blue temp sender, injectors, numerous vacuum hoses, valve adjustments.

Only productive thing I have to say is that 1221 isn't necessarily the O2 sensor, it's tripped if the engine runs lean or rich for a certain time.

[fastair]

Wow, that's encouraging.

[ADEN]

I think O2 signal is not essential for starting to the ECU.Car can start when disconnected.
Check if the signal wire from the plug to the ecu is shorted to ground and that might make ecu go nuts or check the o2 sensor itselt for short.
Wish you luck.
I really hate it when the harness starts to play games with me, The good news that e30' harrness is not big.