ECU fault codes (Opel Vectra A 1994 engine 20NE)

Question

I have really hard start, bad idling, and sometimes engine goes off gradually in about 5 seconds. I've done the paper clip test with the 10 pin ALDL connector and the error codes are:

code 21 Throttle position sensor_high voltage

code 31 Engine RPM signal (crankshaft sensor)_No signal

code 73 Air flow sensor (AFS)_low voltage

I want to add that, I've checked the spark plugs and they're wet of gas, also i looked inside of the cylinders and they are wet too. I've attached a picture of one the spark plugs, they're new spark plugs and they even didn't work for 50 km, but that's the condition of all of the spark plugs. When i clean and dry them the engine starts without any pause, but mostly it doesn't remain the same and it goes off after just 2-3 seconds or it goes to bad idling and then after some time the engine goes off.

Update: all of the fault codes went away after i changed the connectors and connections of the old wires, and the 31 code as @p1ns mentioned was just because i didn't run the test with the engine running. So i don't have any fault codes now, but still abnormal volume of gas injected in the cylinders and i guess that's the reason of hard start and bad idling. As i mentioned before, with dry spark plugs engine starts less than a second but it usually goes off after just 1-3 seconds and the spark plugs becomes completely wet of gas.

Any advice is really appreciated

Answer 1

Code 31 always appears if you do the test not running the engine.

You need to replace the Air Flow meter if code 73 always appears.

Answer 2

I suspect the problem is the air flow sensor. If it can't measure the amount of air going into the engine, it can't know how much fuel to inject. About the only case where it's possible to know how much fuel to inject with a broken air flow sensor is when the engine is warm, and if it has lambda sensor (but that would be the C20NE engine with catalytic converter, not the 20NE engine without).

I had an Opel with C20NE engine long time ago, and it indeed ran rough when not warm, it also gave the air flow sensor error code occasionally.

This engine has a particularly poor air flow sensor. It doesn't use a modern hot wire sensor, but rather has a spring-loaded flap that moves with airflow and controls a rheostat. The surfaces of the rheostat develop poor contact with usage. A replacement sensor could be tricky to find new (and if you find one it's very very expensive), and probably any used part from junkyard has the same problem too.

Indeed, the engine RPM code only means the engine is not running at that particular time. Don't care about it. It will go away if you start the engine.