1222, M42 runs rough or stalls when hot or after long drive.

[techie]

Hey Everyone,
I feel compelled to share this bit of knowledge as this problem plagued me for over 2 years and nowhere else on the web did I ever find the answer.

This problem applies to the E30 M42. 1991 318is

Description:
After running the engine for an hour or more in hot 80+ outside temperatures.
The engine will abruptly run rough, lose power and the ECU will throw a 1222 error as the check engine light comes on. This error is lambda1 out of range, which indicates super rich or lean exhaust gas from the EGO sensor.
Shortly after the check engine light comes on the engine will die or idle rough, until restarted. Upon restarting the engine it will run marginally for about 10-15 minutes, until the EGO sensor is read again, then loop back to the 1222 error and run rough once again.

The cause of the problem:
Faulty ignition coils!
As the coils on the M42 age and rust they can also develop micro scores / traces or even visible cracks in the plastic insulation causing sparks to run along the outside of the coil. This problem is most intensified when the coils heat up under the hood and the cracks in the insulation expand.

The Solution:
Replace the faulty ignition coils (12-13-9-066-468-M618) and wires if necessary. Recommend replacing all the coils at once as for what they cost it’s worth it. This fix was instant gratification for my long drawn out issue.

Notes:
Initially confusing why a faulty coil or two could cause the entire engine to die is what throws off most I think. Especially with the 1222 error code. Technically speaking what happens here is when a coil starts to leak 1 or more cylinder fails to fire, sending un-burnt fuel down the pipe. The EGO interprets this as the engine running too rich and thus proceeds to lean the entire mixture out until the engine dies. Thus the 1222 and also the temporary fix by restarting the car. I hope someone finds this helpful, I wish I could have found such document years ago.

[Jeron]

Good info, thanks.