Ignition coil fault code

[Mathew4]

On my 2008 Auris (71,000 miles), the check engine light came on last week just as I was pulling onto the motorway. I also felt a loss of acceleration. I managed to get it home as the next exit wasn't far and the loss of acceleration was only a few times during the time on the motorway. Once off the motorway the car seemed to be running fine. That night I did a search for things that it could be, and the fuel cap being a possible cause was mentioned. The engine light was still on and stayed on after a number of starts. However after taking the fuel cap off and back on, the light went out. I then took the car out for a test drive and thought it was running okay. That was until after about 10 minutes, then the light came back on, but the car still seemed to be running okay. I turned back for home as soon as the light came on, and was only about 2 minutes from home. However by time I got home, I could feel it was running a little rough. Once home, I tried once more removing the fuel cap off and on, but this time the light stayed on.

My next step was to order a obdii reader, which told me the fault was a P0354. Which is primary/secondary ignition coil D. After looking online, I saw that it could still be a few different things, and one way to see if it is the actual coil is to swap two of them over. Which I did today. By the way, this morning once again opening the fuel cap and putting it back on, made the light go back out. So the fuel cap seems to reset the light when the engine is cold but not when it is warm. It took about 15 minutes of leaving the engine running for it to come back on. Once it was on, I checked the code was still the same one and then cleared it with the obdii scanner.  Then swapped the number 4 coil with one of the others. Hoping that there would be a code now saying that the fault was in the coil number that I had swapped it to. However the light has stayed off. Leaving the car running made no difference, neither has going on a test drive. The sound of the engine sounds the same as it did this morning before I swapped the coils. Maybe slightly rough when revving the engine but really if I wasn't looking for a problem I wouldn't notice and not sure if it was like that before this problem started. Idle seems a bit low at around 600 rpm, but to be honest can't remember what it was before (since the service in February). As the light wouldn't come back on, I tried swapping the coil packs back again, to see if I got the original code, but still the light will not come back on. 

I had the car serviced (intermediate service) at the end of February and then used it for a couple of weeks before lock down. Then it sat until last week (did start it up most weeks).

So my question is if the coil was faulty, would the code come back on after I cleared it with a scanner? Or would it take a certain amount of time before it came back? Also does anyone have any ideas what this sounds like it might be? Could just taking the coil out and putting it back in, really fix the problem? My concern is if I drive it and the fault is still there, that I could be doing damage to the catalytic converter. Normally I would take it into the garage and get them to look at it. But I really don't want to take it in, unless I have to, because of the virus.

 

Edit: The car is a 1.6 Petrol

[eygo]

check the fuel tank breather as it may be blocked,

i'm saying this as you mentioned removing the cap

let the light go out there may of been a vacuum

getting created and stopping the fuel from flowing.

if something spurious has happened this is why the light

came on then it would then probably stay off after resetting

if there is still a fault present then the light will come back on.

if its was a vacuum creating the fault by not having fuel

getting through the managment system

has probably registered the misfire and logged it against

the coil pack in question when in fact there is nothing wrong with the pack

just the lack of fuel.

[Mathew4]

Thank you for the reply and suggestion. Will need to do a search to see how I check the breather. I had thought it strange that if it was a coil that the fuel cap would reset the light. However would a lack of fuel always cause it to be the same coil that registered the misfire? As I said I took the cap off this morning and that reset the light. Then ran the car for about 15 minutes until the light came back. Then checking the code, it showed the fault with the same coil as it had before. Wouldn't a lack of fuel either cause a fault to register on all coils or at least it to be a random one each time?

Before your suggestion, I was thinking that maybe it was something with the pcv value and maybe taking the fuel cap off was letting some pressure out somehow. Then somehow that taking the coils off had let more pressure out of the crankcase. But from my little understanding of how it works, that seems unlikely.

[eygo]

the noise you would of heard when removing the fuel cap wouldn't

be pressure escaping but air being sucked back into the tank,

you know how long it takes for the light to come back on

if you have 1/2 a tank of fuel left or less you could try removing the fuel cap

or just lossening it a little and drive round and see if it happens again.

[eygo]

look for item number 77226A  on the drawing this is the breather pipe

https://jp-carparts.com/toyota/partlist.php?maker=toyota&type=165110&cartype=8&fig=7701