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Old 06-08-2022, 06:17 AM   #1
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Question Intermittant misfire

My car is throwing a P305 intermittently

I swapped out the coil pack and still get a MIL intermittently. It seems to happen more often at low /idle RPM.
It does clear from the dash if I click Ok with the stalk, which it did not do before I changed the coil pack. It also threw the code more frequently before I changed the coil pack.

I am pretty sure the plugs have never been changed ( I bought the car with 80k on it), and there is 112k on the clock. I was thinking that maybe from the misfire, the plug got fouled a little and driving with the plug firing cleaned it a bit

Any ideas?

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Old 06-08-2022, 07:21 AM   #2
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Quote:
Originally Posted by JayG View Post
My car is throwing a P305 intermittently

I swapped out the coil pack and still get a MIL intermittently. It seems to happen more often at low /idle RPM.
It does clear from the dash if I click Ok with the stalk, which it did not do before I changed the coil pack. It also threw the code more frequently before I changed the coil pack.

I am pretty sure the plugs have never been changed ( I bought the car with 80k on it), and there is 112k on the clock. I was thinking that maybe from the misfire, the plug got fouled a little and driving with the plug firing cleaned it a bit

Any ideas?
Always go with the simplest things first.
Change the plugs out.
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Old 06-10-2022, 04:34 AM   #3
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UPDATE

It appears the misfire happens at idle/low rpm only

I have a code reader attached while driving and I am getting a P305 code sometimes but no check engine light on the dash

Haven't had a chance to check/change the spark plug
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Old 06-15-2022, 06:45 PM   #4
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Changed both the coil and plug.
Still get P305 code at low RPM every now and then
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Old 06-15-2022, 08:49 PM   #5
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305 is for cylinder 5, middle cylinder on driver's side bank.

Check all the wiring up to the coil pack for that cylinder (all the way back to the dme).

Truthfully though, if it's only happening at idle, its probably not the wiring or plug. I suspect an injector issue. Run a can of seafoam or techron and see if that helps (the more concentrated the better). Even better would be to pull that injector and bench test it.

Vacuum leaks can also cause misfire, and small leaks cause the most issues at idle, but it would be pretty unusual for it to be confined to only that cylinder. Might not be a bad idea to do a vacuum test though just to be sure.

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Old 06-16-2022, 05:23 AM   #6
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Quote:
Originally Posted by ike84 View Post
305 is for cylinder 5, middle cylinder on driver's side bank.

Check all the wiring up to the coil pack for that cylinder (all the way back to the dme).

Truthfully though, if it's only happening at idle, its probably not the wiring or plug. I suspect an injector issue. Run a can of seafoam or techron and see if that helps (the more concentrated the better). Even better would be to pull that injector and bench test it.

Vacuum leaks can also cause misfire, and small leaks cause the most issues at idle, but it would be pretty unusual for it to be confined to only that cylinder. Might not be a bad idea to do a vacuum test though just to be sure.

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Hadn't thought about the injector, thanks.
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Old 06-24-2022, 04:47 AM   #7
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So after running 2 bottles of Redline Sl-1 fuel system cleaner and a bottle of Royal Purple Max-Clean Fuel System Cleaner no codes for a day with freeway and city stop and go driving.

The codes were only at idle and (knock on wood) after the cleanse, no issue

will see what today brings
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Last edited by JayG; 06-24-2022 at 12:22 PM.
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Old 06-24-2022, 06:53 PM   #8
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Originally Posted by JayG View Post
So after running 2 bottles of Redline Sl-1 fuel system cleaner and a bottle of Royal Purple Max-Clean Fuel System Cleaner no codes for a day with freeway and city stop and go driving.

The codes were only at idle and (knock on wood) after the cleanse, no issue

will see what today brings
Nice!

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