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

All of the spark plugs are in the same condition or worse

  • Have you tried to clear the codes to see what comes back? Oct 11, 2020 at 0:35
  • Thanks @Pᴀᴜʟsᴛᴇʀ2, yes, I've disconnected the battery for some time and reconnect it again but the problem persists.
    – paul
    Oct 11, 2020 at 22:26

2 Answers 2


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.

  • this answer can be improved by adding more details and an explanation of the causes for this error codes to happen. Oct 13, 2020 at 7:43
  • Thanks @p1ns, I'll try these and check about the result. what about the 21 code and abnormal volume of gas in the cylinders? do you have any advice about it?
    – paul
    Oct 13, 2020 at 7:49
  • The code 21 as you said is related to the throttle position sensor. This sensor sends a voltage to the ECU relative to the throttle position. It means again that the ECU detects that an invalid voltage has been present. About excess gas, since the AFM is not working correctly, the air/fuel mix is probably not OK. You should try to replace or fix the AFM and TPS until no engine light appears.
    – p1ns
    Oct 13, 2020 at 8:23
  • Thanks @p1ns, i've updated the question. Do you have any recommendation now?
    – paul
    Oct 13, 2020 at 18:17
  • Sorry man I don't think I can help you anymore. I just wanted to help you with the fault codes thing and hoping that you could solve it after fixing the sensors and checking that no more faults appear. However, if the engine is still stopping and no more fault codes are stored in ECU, you should take the car to a shop so they can search for the problem.
    – p1ns
    Oct 13, 2020 at 21:17

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.

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