Engine jerking and revving, multiple failed ignition coils

Question

This problem started a month ago. My Aveo started revving and jerking when it was sitting at a light on my way home (2 blocks from my house) and the engine light came on. I drove it home. The next day I went to drive it to the mechanic and the engine would not turn over. I had it towed to the shop. They replaced the battery, terminals and the ignition coil.

Less than a month later, we are driving to the beach and the engine starts jerking a revving again and the CEL came back on. We were in a place where we couldn't pull over, so my husband tried to drive it to a shopping plaza. The car would not go over 35mph. We had it towed back to the mechanic. They replaced the ignition coil again (said it was faulty).

Less than a week later, it happened again. The engine is jerking and revving and the car can not shift out of second. This time the engine light is not on. We got it back home (made it 5 miles from when we picked it up)

Do I bother taking it back to the mechanic? or do I see if I can get the engine light to come on? I have no clue of it is a third bad ignition coil or if there is another issue. Without the engine codes, I'm stumped.

What steps can I take to diagnose this issue?

Answer 1

Bad coils are just one of many things that could be to blame.

I'd say stop changing coils. It is highly unlikely that they were the root cause of the problem to begin with.

The symptoms provided are consistent with a misfiring engine. This usually means that there is an issue with the mixture of air and fuel reaching the engine (more on that in a bit).

So how come the car runs fine after returning from the garage?

I have no way of proving it, but this could be explained by the garage resetting the fuel trims.

In some vehicles, disconnecting the battery for a few hours is enough to reset the fuel trims; others require a scan tool. Either way, these fuel trims are re-learnt over time. While relearning, the car may operate well while the fuel trims are reasonable. As they worsen over time, the misfiring will return.

So what could be wrong?

If I were asked to highlight the probable culprits, they would be:

• unmetered air

  So the engine computer is sensing less air than what is actually present. Ask the garage to perform a smoke test on the intake to test this theory.

• faulty lambda sensor(s)

  These sensors are also commonly referred to as O2 sensors. If possible, hook up the vehicle to a scan tool and check if the sensor voltages are flitting between 0.2 and 0.8 V. If they aren't, the lambda sensors will likely need replacing.

• faulty MAF/MAP sensor(s)

  If there are no intake leaks (result of the smoke test), an under-reading sensor can explain why the engine is misfiring.

Please note that this list is not exhaustive, but is a very good place to start hunting down such issues. All the best.

Answer 2

Mechanic changed out the spark plug wires. This stopped the jerking and revving. The engine light came back in after I drove it 20 miles. I requested a smoke test, but I was told that it wasn't necessary. At this point, I'm just going to handle this myself.