Error code p0306 Mis-fire?

[fun173]

Hey everyone.

Since i got the car in August it has had a rough idle. We took it to the dealer and had them replace all the plugs and clean the fuel injectors. After that the car ran a bit better but still had a rough idle.

Now, the check engine light has come on and it is idling very rough, like when we first bought it. I'm not sure what the deal is. Its throwing a p0306 code which I read is a mis-fire in cylinder 6.

I am wondering if the dealer actually changed all of the spark plugs or just decided to do the first 4 because the last 2 are difficult to get to. I think i may have to try to pull the plug out myself to see if they actually did change them. Other than that, I'm not sure what it could be. Any ideas?



P.S. The car is difficult to start while warm and is rough until about 1.5k rpm's and during idle where the needle fluctuates a bit and the car shakes.

P.S.S. Anyone local around Boston who would not mind earning a few bucks and knows how to change the plugs?

[Sean486]

I wonder if that could be a bad coil?

[Freeman]

Originally Posted by Sean486

I wonder if that could be a bad coil?

I thought the same thing because I had a similar issue and it turned out to be a coil.

[icingdeath88]

I'm thinking the same thing. Also, It just dawned on me that that might be the source of my funny idle.

Makes sense because it could have gotten better when the coils were taken off and put back on when the plugs were changed. Then got bad again later. A full set of coils costs quite a bit, but I would definitely try replacing the one that's misfiring.

Which cylinder is #6 anyway? I've still never learned the numbering system for cylinders.

[Green1995SVX]

I agree. You probably either have a bad coil or a torn coil boot.

[Subix]

I had the same issue and it kept getting worse to where the entire car felt like it was quaking. While replacing the bad coil pack fixed it, checking out the other ones... I realize it will only be a matter of time before it re-occurs because of another failing coil pack. (they all seem brittle and slightly cracking). I have yet to pick up the 5 new ones due to other issues and... if it's not broken, don't fix it mentality tends to stick with you when your money is going elsewhere on the car anyways.

Hopefully this summer I can replace the other coil packs. 194k miles (for mine), it only makes sense that they need replaced.

[torxxx]

coil pack dying or you have an injector leaking down after the engine is shut off

My 92 does that. Cold, it starts just fine but after its been warmed up and driven, if you shut it off and restart before the engine is completely cold again, you have to give it some gas and crank for 2 to 10 seconds to get it to bang. Idle stays rough for a few minutes but then smoothens out after the spark plug heats up and unfouls itself.

Pull out #6 spark plug (sucks its the hardest one to check) and see if the plug is wet. If the plug is wet you may have the injector leaking issue

[bwb3]

I just changed my plugs because of a rough idle (especially when warmed up). Runs smoother but still idles rough. 5 of the plugs looked like the plug on the right. Needless to say, I have a coil pack on order.
Do you think the car is running too lean from the looks of the plugs?
Gene

[gbianchi]

2 cents here, always ask for the old parts after having work done, although finding one old plug would be easy to do it can pay off keeping them honest.................G

[torxxx]

no the color of them looks fine. light brown is what you are shooting for with spark plugs. If they were paper white and had chunks missing, I would worry. These aren't forced induction engines, so they don't run as lean as a turbo engine would. If anything I think these engines run a bit rich (well mine does anyways)

[bwb3]

Thanks for the evaluation torxxx. I appreciate now knowing it's burning right.
Gene

[moepower]

i had the same code on cyclinders 4 and 6 but i also had a a code for a crank shaft sensor at the same time replace the crank shaft sensor and the miss-fireing went away